Territorial Disputes

It is well established that some territorial disputes trigger mandatory multilateralism. When the border between two states lacks clear definition, neither state is entitled to impose its preferred solution on the other unilaterally.Footnote ³² Mandatory multilateralism also applies to international disputes over maritime delimitation.Footnote ³³ When states with opposite or adjacent coasts disagree about the delimitation of their exclusive economic zones (EEZs) or continental shelves, they must resolve their dispute “by agreement on the basis of international law” or through third-party arbitration.Footnote ³⁴ In addition, multilateralism is mandatory when a coastal state sets the outer boundaries of its maritime jurisdiction relative to the high seas and deep sea floor. Recognizing that a coastal state's determination of the outer limits of its maritime jurisdiction also demarcates the boundaries of the high seas and the deep sea floor, where the international community has a shared interest, international courts have held that this decision “has always an international aspect” and “cannot be dependent merely upon the will of the coastal State.”Footnote ³⁵ In short, all states are entitled to participate and have their interests duly respected in maritime delimitation decisions that may affect their legal rights. These applications of mandatory multilateralism constitute a “fundamental norm” of international maritime law.Footnote ³⁶

Conflicting Entitlements

Mandatory multilateralism also applies when states assert conflicting entitlements under international law. Consider, for example, the position of states that claim rights to border-straddling natural resources, such as international watercourses and hydrocarbon deposits. In these settings, a state that exercised its sovereign right to exploit a natural resource within its own territory could undermine its neighbor's ability to access or exploit the same resource. Recognizing this problem, the UN General Assembly has called upon states to resolve disputes over shared resources by exchanging information, consulting, and negotiating with one another, with the objective of establishing a multilateral regime to promote conservation and ensure due regard for their respective rights.Footnote ³⁷ States have incorporated the General Assembly's multilateral framework for shared resources into international treaties,Footnote ³⁸ and publicists have recognized that the requirements qualify as customary international law.Footnote ³⁹

States need not have precisely the same legal entitlements to trigger mandatory multilateralism. International courts and tribunals have held that conflicts between asymmetric rights likewise require international cooperation under international law. For example, in the 1974 Fisheries Jurisdiction Cases,Footnote ⁴⁰ the ICJ addressed a conflict between Iceland's “preferential” right to use its own coastal fisheries and other states’ secondary rights, based on historical practice, to fish along the Icelandic coast. The Court rejected Iceland's assertion that the priority accorded to its right under customary international law meant that it was “free, unilaterally, and according to its own uncontrolled discretion, to determine the extent of [its] rights” vis-à-vis other states.Footnote ⁴¹ Instead, Iceland had to “take into account and pay regard to” others’ secondary fishing rights,Footnote ⁴² seeking to reconcile those rights with its own “by agreement.”Footnote ⁴³ Should the states fail to come to terms on a mutually satisfactory solution, they would have to resolve their “disagreement, through the means for peaceful settlement of disputes provided for in Article 33 of the Charter of the United Nations.”Footnote ⁴⁴ Thus, the asymmetric nature of the states’ respective fishing rights did not excuse either state from their obligation under international law to pursue a multilateral solution.

Following the Fisheries Jurisdiction Cases, international courts and tribunals have affirmed repeatedly that mandatory multilateralism applies to other disputes involving conflicting legal entitlements.Footnote ⁴⁵ For example, in the 2009 Dispute Regarding Navigational and Related Rights,Footnote ⁴⁶ the ICJ recognized that Nicaragua was entitled under international law to regulate navigation on the San Juan River, but it nonetheless concluded that Nicaragua could not restrict Costa Rica's secondary rights to use the river for transportation without notifying and consulting with Costa Rica to better understand how proposed regulations would impact Costa Rican nationals.Footnote ⁴⁷ Nicaragua also could not impose visa requirements on Costa Rican vessels, the Court held, because this practice would subject Costa Rica's transit rights to Nicaragua's unilateral discretion.Footnote ⁴⁸ The ICJ explained that these substantive and procedural requirements were based, in part, on the “very subject matter” of the regulations: “navigation on a river in which two States have rights, the one as sovereign, the other to freedom of navigation.”Footnote ⁴⁹ To honor the states’ respective rights, international law required Nicaragua and Costa Rica to proceed in a spirit of multilateral cooperation, each consulting the other and according due regard to the other's legal interests.

Common Resources

Mandatory multilateralism also applies to resources that international law designates as “common areas,” “common heritage,” or “common concerns” of mankind.Footnote ⁵⁰ The concept of common resources originates in the international law of the sea. For centuries, international jurists have affirmed that the high seas constitute a global commons (res communis) outside the scope of national jurisdiction.Footnote ⁵¹ International law therefore prohibits states from regulating activities on the high seas unilaterally. As the 1982 UN Convention on the Law of the Sea (UNCLOS) explains, states must “cooperate with each other in the conservation and management of living resources in the areas of the high seas” by entering “into negotiations” to establish multilateral frameworks for guaranteeing the sustainable exploitation of fisheries and other living resources.Footnote ⁵² By virtue of their placement outside the scope of any individual state's sovereign jurisdiction, the natural resources in these common areas can only be administered properly through norms and institutions that reflect the collective governance of the entire international community.

Since the 1950s, the concept of common areas has expanded from the law of the sea to other important domains. “Outer space, including the moon and other celestial bodies,” constitutes a common resource of mankind under international law,Footnote ⁵³ with the consequence that states must conduct activities in outer space in accordance with “the principle of co-operation,” giving “due regard to the corresponding interests of all other States.”Footnote ⁵⁴ States have also preserved Antarctica as a global commons for peaceful exploration and scientific study,Footnote ⁵⁵ with decisions made through a multilateral consultative process.Footnote ⁵⁶ Like the high seas and deep ocean floor, these resources are designated by law as common areas subject to collective administration by the entire international community, and they trigger mandatory multilateralism.

The international community has endeavored, with mixed success, to designate a variety of other resources as “common heritage” resources that trigger mandatory multilateralism for the purpose of ensuring equitable distribution of a resource. For example, UNCLOS provides that minerals at the bottom of the high seas are the “common heritage of mankind,” and therefore subject to an international condominium (res publica omnium) under multilateral administration.Footnote ⁵⁷ Hence, when a state harvests mineral deposits from the deep sea floor, other members of the international community are entitled under UNCLOS to an equitable share of the proceeds.Footnote ⁵⁸ Other resources that have been designated by treaty as humanity's common heritage include important cultural works, such as great monuments of architecture, art, and history.Footnote ⁵⁹ In each of these settings, some states have resisted efforts to apply the common heritage concept, fearing the limitations that this designation would place on their freedom to act unilaterally.Footnote ⁶⁰ Yet, for present purposes, this practice only serves to underscore that states recognize that once a resource acquires common heritage status, the designation triggers mandatory multilateralism under international law.

In a similar spirit, aspects of the global environment have been characterized as “common concerns of humanity” that trigger requirements of international cooperation.Footnote ⁶¹ Painting with a broad brush, the Rio Declaration on Environment and Development proclaims that states bear a sweeping obligation to “cooperate in a spirit of global partnership to conserve, protect and restore the health and integrity of the Earth's ecosystems.”Footnote ⁶² International treaties, however, tend to define common concerns of humanity more narrowly, leaving room for states to exercise a substantial measure of independent judgment within their respective jurisdiction. For example, the UN Framework Convention on Climate Change (UNFCCC) describes “change in the Earth's climate and its adverse effects” (not the atmosphere or the climate writ large) as a “common concern” of humanity that requires “the widest possible cooperation by all countries and their participation in an effective and appropriate international response.”Footnote ⁶³ Similarly, the Convention on Biodiversity identifies the “conservation of biological diversity” (not animal life per se) as “a common concern of humankind.”Footnote ⁶⁴ By explicitly specifying in treaties that these and other issues constitute common concerns of humanity, the international community has signaled that states’ sovereign rights to exploit resources within their domestic jurisdiction are coupled with a concomitant obligation to cooperate with other states in advancing sustainable development and preventing catastrophic environmental harm. These advances in international environmental law provide further evidence that when common resources of humanity are at stake, international cooperation becomes mandatory under international law.

International Peace and Security

International peace and security is a fourth area where multilateralism is mandatory under international law. A principal purpose of the United Nations is to “maintain international peace and security” by facilitating “effective collective measures for the prevention and removal of threats to the peace.”Footnote ⁶⁵ To further this purpose, the UN Charter empowers the Security Council to coordinate the international community's collective response to emerging threats.Footnote ⁶⁶ Individual member states, in turn, are obligated to cooperate with the Security Council to achieve these collective objectives. Integral to this multilateral framework is the requirement that states “settle their international disputes by peaceful means”Footnote ⁶⁷ and “refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state.”Footnote ⁶⁸ If states cannot resolve their disputes peacefully through negotiation or arbitration, they are obligated to refer the matter to the Security Council.Footnote ⁶⁹ States must also “give the United Nations every assistance in any action it takes” to maintain international peace and security and “refrain from giving assistance to any state against which the United Nations is taking preventive or enforcement action.”Footnote ⁷⁰ The mandatory nature of these duties is underscored by Article 2(6) of the Charter, which charges the United Nations with ensuring that even “states which are not Members of the United Nations” do not imperil “the maintenance of international peace and security.”Footnote ⁷¹ States that flout their duties to cooperate with the United Nations in suppressing threats to international peace and security expose themselves not only to international censure, but also to possible international sanctions and other coercive measures, as directed by the Security Council.Footnote ⁷²

Some international lawyers might object that the Charter's multilateral aspirations for the use of force are undermined by Article 51, which contemplates that states may defend themselves from attack without awaiting Security Council authorization.Footnote ⁷³ In principle, however, a state's “inherent right” of self-defense under Article 51 is consistent with the Charter's commitment to mandatory multilateralism.Footnote ⁷⁴ Self-defense is permissible only when international peace and security have already been ruptured by an actual or imminent armed attack, and only until the Security Council intercedes.Footnote ⁷⁵ The Charter also provides that an act of “self-defense shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council” to prescribe a multilateral response.Footnote ⁷⁶ Moreover, self-defense is constrained by customary requirements of necessity and proportionality, which compel states to take into account the impact of their defensive measures on foreign interests. Thus, even when states act in self-defense, international law channels their response through multilateral norms and processes.

International Human Rights and International Criminal Law

International human rights and international criminal law norms comprise a possible fifth category of mandatory multilateralism. According to the Charter, a core purpose of the United Nations is “[t]o achieve international co-operation in solving international problems of an economic, social, cultural, or humanitarian character, and in promoting and encouraging respect for human rights and for fundamental freedoms for all without distinction as to race, sex, language, or religion.”Footnote ⁷⁷ Although states are primarily responsible for protecting and fulfilling human rights within their own jurisdictions, under the Charter they also “pledge themselves to take joint … action in co-operation with the [United Nations]”Footnote ⁷⁸ to secure “universal respect for, and observance of, human rights and fundamental freedoms for all.”Footnote ⁷⁹

In the United Nations’ infancy, states worked in cooperation with the General Assembly and the UN Economic and Social Council (ECOSOC)Footnote ⁸⁰ to codify international human rights in landmark agreements, such as the Universal Declaration of Human Rights (UDHR),Footnote ⁸¹ the International Covenant on Civil and Political Rights,Footnote ⁸² and the International Covenant on Economic, Social and Cultural Rights.Footnote ⁸³ Over the past several decades, international cooperation has evolved significantly, with the Security Council using its authority under Chapter VII of the Charter to mandate collective responses (e.g., economic sanctions, travel restrictions, military action) to serious breaches of international human rights and international criminal law norms (e.g., genocide and crimes against humanity).Footnote ⁸⁴ When the Security Council addresses a humanitarian crisis in this manner, conventional wisdom now holds that states must cooperate with the Security Council's efforts to promote universal respect for international human rights and international criminal law.Footnote ⁸⁵

Customary international law may also be in the process of developing positive duties of cooperation for addressing serious breaches of international human rights and international criminal law. In its influential Articles on State Responsibility for Internationally Wrongful Acts (the Articles), the UN International Law Commission (ILC) has endorsed the view that states must “cooperate to bring to an end through lawful means any serious breach” “of an obligation arising under a peremptory norm of general international law.”Footnote ⁸⁶ The ILC's commentary accompanying the Articles acknowledges that reasonable minds might fairly question whether “[customary] international law at present prescribes a positive duty of cooperation,” and it concedes that the Articles’ articulation of this duty “may reflect the progressive development of international law.”Footnote ⁸⁷ Nonetheless, the ILC's commentary stresses that “in fact such cooperation, especially in the framework of international organizations, is carried out already in response to the gravest breaches of international law.”Footnote ⁸⁸ As evidence of state practice and opinio juris continues to accumulate in the future, the ILC's conclusion that customary international law requires states to cooperate with one another to address serious abuses, though somewhat vague and controversial today,Footnote ⁸⁹ may eventually become the prevailing view.Footnote ⁹⁰

Even if a positive duty of cooperation never crystallizes in customary international law, the fact remains that states are already subject to duties of mandatory multilateralism when it comes to promoting international human rights and enforcing international criminal law. Under the Charter, all states have committed to take action, individually and jointly in cooperation with the United Nations, for the purpose of promoting universal respect for human rights. At a minimum, therefore, states bear an obligation to cooperate with the Security Council's multilateral initiatives to suppress “the gravest breaches of international law.”

* * * *

As these examples illustrate, mandatory multilateralism has become an important feature of international law that arises in diverse subfields, from territorial disputes to environmental protection to the prevention of mass atrocities. Where mandatory multilateralism applies, states are legally obligated to cooperate with their peers to address issues of global concern through consultation, negotiation, and, if necessary, third-party dispute resolution. Mandatory multilateralism is reflected in the Charter's requirement that states peacefully resolve any disputes that are “likely to endanger the maintenance of international peace and security,”Footnote ⁹¹ but its reach extends well beyond such disputes. Even if no threat to international peace and security is immediately foreseeable, international law still requires states to cooperate with one another to resolve disputes concerning undefined borders, conflicting entitlements, common resources, or serious breaches of international human rights and international criminal law. As the ICJ has explained, the duty to cooperate arises in these settings from the “very subject-matter” of the disputes,Footnote ⁹² and not simply because hostilities are likely to follow.

The emergence of mandatory multilateralism requires some explaining. Why does international law sometimes mandate multilateralism rather than let states decide for themselves? In Part III, we develop an interpretive theory that explains why multilateralism is sometimes mandatory under international law. We argue that mandatory multilateralism is not an anomalous feature of a few isolated international regimes; rather, it emanates from two foundational and organizing principles of contemporary international law: sovereign equality and joint stewardship.Footnote ⁹³

Sovereign Equality

International law's venerable principle of sovereign equality—par in parem non habet imperium—means literally “equals do not have authority over one another.”Footnote ⁹⁴ Analogizing to the moral status of individuals in the state of nature, Vattel offered a classic statement of the principle:

For Vattel, might can never make right—“Strength or weakness … counts for nothing”—and so “a small Republic is no less a sovereign state than the most powerful Kingdom.” In the interwar period, Edwin DeWitt Dickinson developed a similar view, deriving sovereign equality from the formal international legal personality of states and arguing that “[i]nternational persons are equal before the law when they are equally protected in the enjoyment of their rights and equally compelled to fulfill their obligations.”Footnote ⁹⁶ This conception of sovereign equality, and the conception on which we rely, is formal rather than substantive in that it goes to questions of legal status and standing rather than, say, the allocation of resources. Nonetheless, we shall see that this formal conception has concrete, substantive implications.

The movement of sovereign equality from Vattel to modernity was far from smooth and continuous. In the nineteenth and early twentieth centuries, the United States and European powers either explicitly or implicitly placed national interests ahead of aspirations for an international order premised on equality.Footnote ⁹⁷ For example, President Theodore Roosevelt famously rejected sovereign equality and viewed the United States as the world's policeman.Footnote ⁹⁸ Similarly, although the Peace Conferences held at The Hague in 1899 and 1907 were formally organized around the idea of sovereign equality, in practice the Great Powers dominated.Footnote ⁹⁹ Great Power domination was also evident in the Peace Conference at the end of World War I, and in the design and creation of the United Nations after World War II,Footnote ¹⁰⁰ notwithstanding President Franklin Delano Roosevelt's “Good Neighbor Policy,” which articulated “nothing less than a full-throated rejection of the long-held American right to intervene in the affairs of its southern neighbors.”Footnote ¹⁰¹ Nowhere is Great Power dominance more evident than in the structure of the UN Security Council, with five permanent and veto-empowered members drawn from the victors of World War II.Footnote ¹⁰² Nonetheless, the UN Charter and the international legal order it inaugurated gave the principle of sovereign equality new significance.

Article 2(1) of the Charter stipulates that the United Nations itself “is based on the principle of the sovereign equality of all its Members.” Footnote ¹⁰³ Various elements of this principle were later specified and enshrined in the UN General Assembly's Declaration on Principles of International Law Concerning Friendly Relations and Co-operation Among States in Accordance with the Charter of the United Nations (Friendly Relations Declaration).Footnote ¹⁰⁴ The Friendly Relations Declaration expressly provided that all states are “judicially equal” and that each “enjoys the rights inherent in full sovereignty.”Footnote ¹⁰⁵ In effect, the Declaration took a middle path between Eastern-bloc and non-aligned states that viewed international cooperation as a general requirement of customary international law, and Western states that viewed international cooperation to be legally binding only if codified in a treaty.Footnote ¹⁰⁶ In addition to a rich conception of sovereign equality, the Friendly Relations Declaration affirmed “[t]he principle of equal rights and self-determination of peoples,” the “duty of States to co-operate with one another in accordance with the Charter,” and that “States shall settle their international disputes by peaceful means.”Footnote ¹⁰⁷ Put slightly differently, the Declaration deployed the principle of sovereign equality to reconcile international law's commitments to the autonomous self-determination of free and equal peoples, on the one hand, and a Charter-based legal framework within which international cooperation and peaceful dispute resolution is to take place, on the other.

The principle of sovereign equality also figures prominently in numerous international judgments. The ICJ has held that the rule of sovereign immunity “derives from the principle of sovereign equality of States,” such that “[e]xceptions to the immunity of the State represent a departure from the principle of sovereign equality.”Footnote ¹⁰⁸ The foundational status of the principle was implicitly affirmed in Judge Charles Andre Weiss's dissent in the Permanent Court of International Justice's (PCIJ) Case of the S.S. Lotus. Footnote ¹⁰⁹ Judge Weiss reasoned that “the rule sanctioning the sovereignty of States” is one “which is paramount and which does not even require to be embodied in a treaty” because if this rule is not valid “no international law would be possible, since the purpose of [international] law precisely is to harmonize and reconcile the different sovereignties over which it exercises sway.”Footnote ¹¹⁰ Although the judges of the PCIJ divided over the outcome of the case, all accepted the principle that the international community's “different” sovereignties are equal sovereignties.

To be sure, sovereign equality does not entail that sovereigns all possess the same primary rights and obligations at international law. Much of international law arises from treaties that states can elect to enter into or not at their discretion. Thus, states can choose whether or not to acquire the rights and assume the obligations that flow from the ratification of such treaties. But sovereign equality does entail, as U.K. Preuss puts it, that “no state is superior to any other state, and all states are equals with respect to their status in the plurality of states … . [T]hey are equally independent. Therefore, the states’ equality can rightly be regarded as a ‘corollary of sovereignty.’”Footnote ¹¹¹

Prior to the League of Nations and the United Nations,Footnote ¹¹² relations between states were horizontal (at least formally, in a de jure sense), and so the equal independence of states could be understood purely in terms of each state's horizontal independence from others. However, with the development of the United Nations and other post-World War II international institutions, relations between states have attained a measure of constitutionalization in part because supra-state entities exercise international lawmaking or adjudicative powers over states within their respective jurisdictions.Footnote ¹¹³ In this context, horizontal independence is still significant, but with collective decision making over certain matters now allocated to hierarchically superior institutions such as the Security Council and the WTO, the principle of sovereign equality needs also to reflect the equal status of states in their vertical relations to international institutions. A shared concern in both horizontal and vertical relations is the status of smaller or weaker states with formal de jure equality but lacking de facto status and influence. As Brad Roth puts it: “To speak … of ‘sovereign equality’ … is to speak principally of the sovereignty of weak states.”Footnote ¹¹⁴ That is, although the conception of equality at issue is formal rather than substantive, the legal equality it affords enables weaker states to make legal claims that can have substantive effects.

International legal materials—treaty law, customary law, judicial decisions, and scholarship—disclose two distinct approaches to sovereign equality. The conventional view reflects a predominantly voluntarist model under which states are bound to resolve disputes through multilateral means only if they have ratified a treaty so as to undertake specific obligations. An alternative view—the view defended here—is a constitutionalist model according to which states, within certain domains calling for international cooperation, are subject to positive multilateral obligations—e.g., obligations to negotiate in good faith and resort to a third-party if necessary—to which they may not have formally consented. We discuss these models in turn, and then discuss the Lac Lanoux Arbitration as a case study.

Voluntarism

The voluntarist view of sovereign equality gives pride of place to the thought that sovereigns exercise power without being subject to the authority of any other sovereign—as “uncommanded commanders.”Footnote ¹¹⁵ As the PCIJ put it in the Status of Eastern Carelia case, “[i]t is well-established in international law that no State can, without its consent, be compelled to submit its disputes with other States either to mediation or arbitration, or any other kind of pacific settlement.”Footnote ¹¹⁶ On this view, sovereigns are supreme within their jurisdiction and independent in their relations to other sovereigns. The voluntarist view captures some of international law's prohibition on unilateralism in that no sovereign state is entitled to dictate terms to another, for such an entitlement would mark a compromise of the formal principle of sovereign equality. For voluntarists, the equal independence of states implies that state consent is the sine qua non—the necessary and sufficient normative condition—of international obligation.

Voluntarists typically use the so-called “Lotus principle” as their doctrinal touchstone.Footnote ¹¹⁷ The principle is drawn from the Lotus majority judgment,Footnote ¹¹⁸ the essence of which Prosper Weil summarizes as “whatever is not explicitly prohibited by international law is permitted.”Footnote ¹¹⁹ The PCIJ held that “[t]he rules of law binding upon States … emanate from their own free will as expressed in conventions or by usages generally accepted as expressing principles of law … . Restrictions upon the independence of States cannot therefore be presumed.”Footnote ¹²⁰ The Court also declared that states under international law enjoy “a wide measure of discretion, which is only limited in certain cases by prohibitive rules; as regards other cases, every State remains free to adopt the principles which it regards as best and most suitable.”Footnote ¹²¹ Thus, Weil claims, the Lotus principle is grist for the mill of a “consensualist and voluntarist conception of international law,” a conception under which states “are bound by a rule of law only because, and to the extent that, they have consented to it. Freedom to act remains the basic principle.”Footnote ¹²²

A significant weakness of this approach is that the institutional practices of international law have increasingly eclipsed voluntarism's normative commitments. As discussed in Part II, mandatory multilateralism has proliferated across numerous settings. In cases of territorial disputes and conflicting entitlements, for example, the requirement to resolve disputes through impartial third-party processes can be explained by the anti-unilateralist principle that no person may be judge and party to the same cause (nemo iudex in sua causa). The very idea of one party holding a legal entitlement to adjudicate its dispute with another would flagrantly violate the principle of sovereign equality. In short, voluntarism cannot account for many fields of international law in which mandatory multilateralism is the norm.

There are significant conceptual problems with voluntarism, too. Recall that an attraction of the voluntarist theory is that it purports to subscribe to international law's prohibition on unilateralism under which no state can impose terms on another: no state can impose terms on another because no state can be bound except by its own voluntary acts. Put another way, states are only subject to legal rules or norms to which they consent, from which it follows that consent is the only means of establishing a rule or norm under voluntarism. Yet, by ceding to non-consenting states a potentially unlimited liberty-right of action—the absolute discretion of the uncommanded commander—voluntarism cedes to these states the liberty-right to decide for themselves the terms on which they will interact with others, regardless of whether the counterparty consents. If a recalcitrant state refuses to agree to fair and equal terms consistent with sovereign equality, voluntarism lacks the resources to censure that state from a legal point of view. Under voluntarism, the recalcitrant state will have breached no legal rule to which it was subject. Thus, while voluntarism prohibits one state from creating obligations for another without the other's consent, voluntarism alone provides no legal resources to condemn a predatory state that seeks to infringe, for example, another state's territorial integrity or political independence.

Our point is not to equate voluntarism with unilateralism, but rather to explain why voluntarism, taken seriously, may permit unilateralism within the conception of the international legal order it endorses. It follows that voluntarism cannot explain sovereign equality because sovereign equality denotes an equal right to external and internal self-determination—a right to equal independence—and this formal equality right implies (as we explain immediately below) substantive reciprocal duties of non-interference and non-domination.

Constitutionalism

A constitutional model of sovereign equality avoids this pitfall while affirming a robust prohibition on unilateralism. On a constitutional reading of sovereign equality, international law both empowers states as international legal actors as well as constrains them in their dealings with other states and non-state actors, including citizens and non-citizens. There is now a considerable literature on the constitutionalization of international law, some of which characterizes this approach to international law as a “mindset” or “sensibility,”Footnote ¹²³ while others note that international constitutionalism shares with its democratic national counterparts core commitments to human rights, democracy, and the rule of law.Footnote ¹²⁴ For our purposes, the constitutional perspective offers a congenial framework within which international law empowers states by recognizing them as the de jure governors of their people at the domestic level and as the de jure representatives of their people in international affairs. This recognition enables states to establish political and legal order nationally and to enter into binding treaties and otherwise represent their people internationally. In their international dealings, however, states are subject to reciprocal limits of a constitutional nature that reflect the equal status of both their sovereign powers and independence vis-à-vis one another.

The dissenting opinion of Judge Bernard Loder in Lotus provides an especially clear account of this constitutional conception of sovereign equality. Judge Loder asserts that states relate to each other on terms of “mutual independence.”Footnote ¹²⁵ It follows from the “independence and sovereignty” of states “that no municipal law … can apply or have binding effect outside the national territory.” Footnote ¹²⁶ To emphasize that he takes this “fundamental truth” to be constitutional in nature—that is, partially constitutive of the structure of international legal order—Loder underlines that it “is not a custom but the direct and inevitable consequence of its premis[e]” (i.e., the “independence and sovereignty” of different states).Footnote ¹²⁷ For states to be sovereign they must be independent, and for them all to be independent, they must be independent mutually or equally. At the heart of Loder's opinion, then, is the constitutional insight that sovereignty implies independence, and that universal independence implies mutual or equal independence. Independence is a necessary condition of sovereignty, while sovereign equality is a necessary condition of universal independence. One sense in which all sovereigns are equal is that none are entitled to dictate terms to others unilaterally, and conversely, none can be made to suffer such terms. This is also the reason sovereign states (in principle) are independent: none depends on the permission of another to exercise domestic or international public functions.

Independence under constitutionalism denotes a form of freedom or liberty. In our view, the liberty of independence has two constitutive elements: a liberal principle of non-interference and a republican principle of non-domination.Footnote ¹²⁸ The principle of non-interference prohibits states from wrongfully interfering with each other through any unilateral act that infringes the legal interests or authority of other states. We define “unilateral act” as one performed by an actor who explicitly or implicitly asserts an entitlement to determine solely the legality of the act. Military aggression is a vivid example of wrongful interference, since one state violates the territorial integrity of another through the unilateral use of force. But other unilateral acts would count as well, including acts that would not count as a “use of force” under international law. For example, a state would violate the principle of non-interference by dictating the outcome of a border dispute, or by insisting on plainly unfair terms of participation in a necessarily collective endeavour, such as the protection of a migratory and endangered species. A simple refusal to negotiate a matter that calls for multilateralism is likewise a wrongful interference, since it contests the authority of other states to negotiate jointly fair terms of cooperation for all concerned.Footnote ¹²⁹ Depending on the context, a refusal to negotiate may be indistinguishable from the position of a holdout who seeks unfair terms in a project of common concern that can succeed only if all or nearly all affected parties take part. A powerful holdout can dominate weaker parties who, in the circumstances, are better off taking an unfair deal rather than living with no deal at all.

The principle of non-intervention can be seen as a salient legal expression of the normative principle of non-interference. The most general formulation of this legal principle in the UN Declaration on Non-Intervention states that “[n]o state has the right to intervene, directly or indirectly, for any reason whatever, in the internal or external affairs of any other State.”Footnote ¹³⁰ The Declaration specifically decries “armed intervention” as a prohibited form of conduct, as well as “the use of force to deprive peoples of their national identity” or efforts “directed towards the violent overthrow of the regime of another State.”Footnote ¹³¹

The Declaration makes clear, however, that the principle of non-intervention is wider than the principle of non-interference. Specifically, the Declaration avows that threats of unilateral acts—and not just unilateral acts themselves—are legally wrongful. The Declaration stipulates that “attempted threats against the personality of the State or against its political, economic and cultural elements, are condemned.”Footnote ¹³² States may not “use or encourage the use of economic, political or any other type of measures to coerce another State in order to obtain from it the subordination of the exercise of its sovereign rights or to secure from it advantages of any kind.”Footnote ¹³³ And finally, linking the prohibition of threats to self-determination and the protection of human rights, the Declaration provides that “[a]ll States shall respect the right of self-determination and independence of peoples and nations, to be freely exercised without any foreign pressure, and with absolute respect for human rights and fundamental freedoms.”Footnote ¹³⁴ Because the principle of non-interference explains exclusively the way actual and wrongful unilateral acts compromise freedom, it cannot explain how certain unrealized threats of those acts compromise freedom.Footnote ¹³⁵ For an account of the wrongfulness of threats and their infringement of liberty, we need the republican principle of non-domination.

For republicans, domination consists in subjection to the arbitrary will of another and is the chief cause of unfreedom.Footnote ¹³⁶ In the classic example of the slave and benevolent slave master, republicanism invites us to imagine a master who wishes only the best for her slave. She treats him like family, supports his hopes and aspirations, encourages his projects, and so on. At no time does the master act on the slave-owning prerogatives she possesses. In short, the master does not interfere with, but rather supports, the slave and his choices. Nonetheless, the slave is still unfree, republicans assert, because the master is entitled to crack the whip at any time, for any reason (including malicious or spiteful reasons), and to do so with impunity. Republicans point out that this asymmetrical power structure ordinarily leads to bowing, scraping, and a constant sense of unease (if not terror) on the part of the dominated party.Footnote ¹³⁷ But the distinct evil of domination—the evil and unfreedom suffered by the slave of the benevolent master—is simply subjection to the looming threat of arbitrary force against which there is no recourse.

When the Declaration on Non-Intervention prohibits “threats” against a state's “personality,” or against its “political, economic, and cultural elements,” the Declaration puts into positive legal form the principle of non-domination. A state's personality is the law-created artificial entity to which the words and actions of the state's representatives are attributed when they act in the name of the state.Footnote ¹³⁸ Consequently, certain threats against the state's personality may constitute existential threats. The threat of military aggression and occupation is this kind of threat. And threats against a state's “political, economic, and cultural elements” are likewise threats of wrongful unilateralism. These may threaten to appropriate things that do not belong to the threatening state, or they may threaten valued public goods in order to impose terms on the weaker state (e.g., accept the terms we offer or we will block your water supply), or they may threaten to end or refuse negotiations with respect to a common resource or some other matter of common concern. The threats are arbitrary in the sense that they aim to secure through a unilateral assertion of will the “subordination” of another state or the gaining of “advantages” to which the dominating state has no entitlement.

Together, therefore, the principles of non-interference and non-domination explain the principle of non-intervention's prohibition of both unilateral acts and threats of unilateralism. The principle of non-intervention in turn lends content to the ideal of mutual independence of sovereign states. The realization of this ideal expresses in practice the core normative requirements of the concept of sovereign equality.

In some contexts, mutual independence and sovereign equality require international cooperation, without which some states would interfere with or dominate others. Mandatory multilateralism is the institutional framework that makes international cooperation possible in a way that respects the independence and sovereign equality of all states. For example, when coastal states confront unsettled questions of maritime delimitation, no individual state can claim the prerogative to resolve the question on its own without dominating other states by threatening to subject them to its unilateral will. Even if a state acted in perfectly good faith, establishing maritime boundaries that were objectively favorable to its neighbors, its unilateral decision making would undermine other states’ formal and equal independence by arrogating to itself a prerogative and standing not held by others. Mandatory multilateralism resolves this and like problems of unilateralism by imposing positive duties of cooperation that safeguard the integrity of formal sovereign equality.

As should now be evident, running through all of these principles and concepts is the prohibition on unilateralism that Hans Kelsen connected directly to sovereign equality and proposed as the basis of international legal order. “Sovereignty in the sense of international law,” Kelsen wrote, “can mean only the legal authority or competence of a State limited and limitable only by international law and not by the national law of another State.”Footnote ¹³⁹ To see how this might work in practice to underwrite positive duties of international cooperation, we discuss next the Lac Lanoux ArbitrationFootnote ¹⁴⁰ as a case study on mandatory multilateralism.

Case Study: The Lac Lanoux Arbitration

Lac Lanoux concerned the rights of France and Spain respectively to the waters flowing from Lake Lanoux in the Pyrenees.Footnote ¹⁴¹ The lake is situated entirely in France, but its waters flow into the Carol River that enters Spanish territory after flowing some twenty-five kilometers through France.Footnote ¹⁴² The Treaty of Bayonne of 1866, completed by an Additional Act that same year, established the Franco-Spanish border and contained provisions that regulated the use of common waters.Footnote ¹⁴³ Article 8 provided that “standing and flowing waters … are subject to the sovereignty of the State in which they are located.”Footnote ¹⁴⁴ Article 11 contemplated a situation in which works in one state might affect waters in the other:

France sought to divert some of the waters from Lake Lanoux to develop a hydroelectric project, undertaking to return the diverted waters to the Carol River (the natural destination of those waters) by means of an engineered tunnel.Footnote ¹⁴⁶ Spain objected to the proposed project, arguing, inter alia, that Article 11 required France to obtain Spain's consent before proceeding with its project.Footnote ¹⁴⁷ In response, France invoked Article 8 of the Treaty of Bayonne, which gives jurisdiction over “standing and flowing waters” to “the State in which they are located,” and it insisted that in any event all the water diverted from the Carol River would be returned to it prior to the river crossing the frontier with Spain.Footnote ¹⁴⁸ Nonetheless, as the International Law Commission has noted, throughout the ensuing dispute the states’ respective obligations “to negotiate the apportionment of the waters of [the] international watercourse was uncontested, and was acknowledged by France not merely by reason of the terms of the Treaty of Bayonne and its Additional Act, but as a principle to be derived from the authorities.”Footnote ¹⁴⁹

The Tribunal rejected, however, Spain's demand that France obtain its consent. The Tribunal concluded that if the Spanish position were upheld, it would have as its consequence, in the event an agreement was not reached, “that the state which is normally competent has lost its right to act alone as a result of the unconditional and arbitrary opposition of another State. This amounts to admitting a ‘right of assent,’ a ‘right of veto,’ which at the discretion of one State paralyses the exercise of the territorial jurisdiction of another.”Footnote ¹⁵⁰ Put slightly differently, the state with the veto would have unilateral power over the state “which is normally competent.” Instead of according Spain a veto, the Tribunal opted for a compromise position, but one that still carried with it legal obligations.

The Tribunal held that France could not treat Spanish interests with indifference, but rather had an obligation to negotiate with Spain in good faith.Footnote ¹⁵¹ In this context, “the reality of the obligations thus undertaken is incontestable and sanctions can be applied in the event, for example, of an unjustified breaking off of the discussions, abnormal delay, disregard of the agreed procedures, systematic refusals to take into consideration adverse proposals or interests, and, more generally—in cases of violation of the rules of good faith.”Footnote ¹⁵² The Tribunal stressed the “necessity to reconcile [conflicting interests] by mutual concessions,”Footnote ¹⁵³ and that to this end “there would thus appear to be an obligation to accept in good faith all communications and contracts which could, by a broad comparison of interests and by reciprocal good will, provide States with the best conditions for concluding agreements.”Footnote ¹⁵⁴

More specifically still, the Tribunal held that it would not be enough for the upstream state to engage in a box-ticking exercise “such as taking note of complaints, protests or representations made by the downstream State.”Footnote ¹⁵⁵ Instead, the Tribunal found that “the upstream State is under the obligation to take into consideration the various interests involved, to seek to give them every satisfaction compatible with the pursuit of its own interests, and to show that in this regard it is genuinely concerned to reconcile the interests of the other riparian State with its own.”Footnote ¹⁵⁶ In the end, the Tribunal concluded that France had satisfied this obligation by negotiating in good faith and giving reasonable consideration to Spanish interests by agreeing to restore the waters diverted to the Carol River in a manner that would best accommodate Spanish agriculture.Footnote ¹⁵⁷

Because France's efforts were realized within a flexible but mandatory legal framework, Spain was not subject to unilateralism on the part of France, notwithstanding the fact that France alone was exercising sovereign rights over the waterway. Rather, Spain and France participated as equals in a process of mandatory multilateralism. Although Spain did not obtain a veto, it did obtain a right to meaningful consultation and accommodation, and that right provided a bulwark against unilateralism. More particularly, both the denial of the veto to Spain and the right to consultation and accommodation it obtained reflected the principles of non-interference and non-domination. Regarding the veto, the Tribunal worried that if Spain had such a right, Spain could dominate France's decision making over the use of its waterways.Footnote ¹⁵⁸ Conversely, the detailed dicta on France's obligations to take account of Spanish interests demonstrate the Tribunal's preoccupation to ensure that France's dominion over an upstream waterway was not used to interfere arbitrarily with Spanish interests, or threaten such interference.Footnote ¹⁵⁹ A major Spanish argument was that France's conversion of a natural waterway was wrongful because the conversion would make Spain dependent on France for waters from Lake Lanoux.Footnote ¹⁶⁰ The Tribunal did not reject the Spanish argument on principle, but on the grounds that the facts did not bear it out: France would injure herself considerably by diverting waters from the tunnel.Footnote ¹⁶¹ In other words, France's only possible threat would be an empty threat, so there was no genuine prospect of France dominating or interfering with Spain. The process of mandatory multilateralism and its positive duties of cooperation provided for the mutual independence of both states.

Joint Stewardship

We next consider how the principle of sovereign equality is complemented by the idea of joint stewardship—a framework for apprehending cases where the care of a common concern is expressly consigned (usually via treaty) to multiple parties. In international law, joint stewardship may be understood as the possession and institutionalization of legal authority over a particular territory or subject matter by two or more international legal actors, usually states. Central to this conception of joint stewardship is, first, an idea of public and legal authority, and second, the thought that this form of authority may be exercised only through the cooperative efforts of two or more parties. On this understanding, private entities (e.g., private firms or organizations) cannot combine forces to provide joint stewardship, since private entities by definition are not public. Nor can a single public international actor (e.g., a single powerful state) exercise joint stewardship. Only multiple public international actors can do so.

International law typically uses treaties to allocate joint stewardship over matters of global concern, such as the high seas, Antarctica, outer space, and resources from the deep sea floor.Footnote ¹⁶² Understood to be part of a global commons over which no one state has exclusive jurisdiction, these common resources are subject to joint stewardship regimes that have both negative and positive dimensions. The negative dimension prohibits states from asserting or exercising exclusive jurisdiction over the relevant resources. Yet international law does not generally treat the resources in question as inaccessible to humanity. Rather—and this is the positive dimension—international law calls on states to negotiate in good faith the terms on which common resources may be used collectively. International cooperation is necessary in the context of common resources to ensure that no state is able to dominate its peers by subjecting these resources to its unilateral will.

Implicit to this positive dimension is international law's allocation to states of standing to represent their peoples in international negotiations and the creation of institutions that are premised on joint stewardship. While much has been written about the diminution of the state's salience in international law,Footnote ¹⁶³ states remain the primary entities that international law authorizes to represent their people in international affairs. States thereby possess legal authority to enter into binding agreements such as UNCLOS. In the case of UNCLOS in particular, the treaty crystallizes joint stewardship through mandatory multilateralism, in part, by requiring states to seek agreement on maritime delineation “on the basis of international law … in order to achieve an equitable solution.”Footnote ¹⁶⁴ If states cannot reach agreement, they are required to pursue third-party dispute resolution.Footnote ¹⁶⁵

As we saw in Lac Lanoux, and as we will see in greater detail in Parts IV and V, the requirements of mandatory multilateralism include substantial duties to take seriously the interests of foreign nationals. These duties make sense only if the interests of other states’ nationals are legally relevant to states whose principal responsibility is to advocate on behalf of their own nationals. We have argued elsewhere that it is possible to explain state duties to extraterritorial foreign nationals if we view states as occupying two positions as public fiduciaries.Footnote ¹⁶⁶ The first is as a local fiduciary of their people—citizens and non-citizens—within their territory or with a special connection to it, such as extraterritorial citizens or permanent residents. The second position is as a global fiduciary of humanity. Under this conception of the state's dual roles, the state's main responsibility is to govern and represent its people. It is the state's global position as a fiduciary of humanity, however, that explains not merely the duties it owes to non-nationals (duties that may conflict with the interests of its people), but also the authority of the state to interact with them and their international representatives—other states—as a joint steward of humanity.

Eyal Benvenisti makes a similar claim, arguing that sovereigns can be understood to be “trustees of humanity,” and as such may be understood to have “modest” duties to foreign nationals that include giving them a voice and taking their interests into account “if doing so is costless [to sovereigns] or … in cases of catastrophe.” ^{Footnote 167} In other words, in the standard case, a sovereign's duties to outsiders arise if the outcome reflects what Benvenisti calls a “restricted Pareto outcome—namely, an outcome from which ‘one benefits and the other sustains no loss,’ with no compensation.”Footnote ¹⁶⁸ He suggests that under the UDHR state parties are duty bearers, but because there is no allocation of responsibilities among them, “the entire system of state sovereignty is subject to the duty to respect human rights.”Footnote ¹⁶⁹ There is much to admire in Benvenisti's approach, though in our view sovereigns may owe duties to foreign nationals even if there is some cost, as there was in Lac Lanoux. Footnote ¹⁷⁰ Indeed, the promise of giving outsiders a voice may prove illusory if reasonable outsider claims can be rightfully denied because they impose a minor cost on the putative duty-bearer.

In some cases, such as international refugee law, states interact with other states to set global or regional policy,Footnote ¹⁷¹ while at the operational level they may interact directly with asylum-seeking outsiders. In other cases, however, joint stewardship arises where international law (ordinarily treaty law) designates a matter of global concern, such as the protection of endangered species, as a common concern for humankind. In these contexts, joint administrative authority is shared by all states, and all states stand in a symmetrical relation of sovereign equality to one another. Because joint authority is shared by states over collective regimes that govern global public goods, states can only exercise joint authority on behalf of humanity (or, at least, on behalf of the transnational group implicated by the relevant transnational good). And because international law regards states as equals within collective regulatory regimes, joint stewardship in this context necessarily takes the form of mandatory multilateralism.

We can bring the contribution of joint stewardship to mandatory multilateralism into sharper relief by comparing it to the role played by sovereign equality. As discussed above, the principle of sovereign equality provides for the mutual independence of states by imposing reciprocal limits on their interactions with one another. The principle supplies a bulwark against unilateralism by prescribing non-domination and non-interference as juridical ideals to frame interstate relations. Mandatory multilateralism is a unified institutional expression of those anti-unilateralist ideals in contexts that call for international cooperation but which are not subject to a comprehensive regulatory regime (e.g., Lac Lanoux). Joint stewardship, in contrast to sovereign equality, attends to international regimes that are premised on collective administration by the entire international community or a substantial and multinational segment of it. Mandatory multilateralism in these settings expresses at the institutional level a form of joint stewardship that protects states, nationals, and foreign nationals from domination and abuse at the hands of individual states. It follows that if participation in a multilateral regulatory regime is truly mandatory, then a failure to participate on equal terms constitutes a unilateral assertion of will and an arrogation by the recalcitrant state of a prerogative not shared by others.

Explaining Mandatory Multilateralism

Sovereign equality is ultimately a necessary and sufficient condition of mandatory multilateralism in contexts where states need to cooperate to ensure their mutual independence, but which are not subject to a comprehensive regulatory regime. Joint stewardship, in contrast, provides necessary and sufficient conditions for mandatory multilateralism in contexts where international law has established a comprehensive regulatory regime to administer a matter of global or transnational concern. These organizing principles illuminate the scope of mandatory multilateralism.

Some international disputes do not trigger mandatory multilateralism because international law supplies a controlling rule of decision or assigns decision making authority exclusively to one side. For example, states are entitled to veto foreign appropriations of their territoryFootnote ¹⁷² and foreign infrastructure projects that would impede their transit through international straits.Footnote ¹⁷³ States can waive rights of this kind. Other entitlements, however, are not subject to waiver or abridgment under any circumstances. In international law, these rules include jus cogens norms, such as the prohibitions against torture and genocide.Footnote ¹⁷⁴ Where applicable, indefeasible entitlements such as these leave no room for further multilateral deliberation, although heated debate attends the questions of which norms count as peremptory and the content of those norms.Footnote ¹⁷⁵ Thus, when international disputes are governed by dispositive norms, international law does not mandate additional international deliberation or interest-balancing. Parties to such disputes may have thin legal duties to communicate with other states and resolve their disputes peacefully, but they are not ordinarily obligated to negotiate toward a mutually acceptable solution.Footnote ¹⁷⁶ Negotiation is unwarranted in these cases because, through its allocation of rights or recognition of other dispositive norms, international law eschews unilateralism by imposing a public legal order of reciprocal limits on all.

Many international controversies cannot be resolved, however, through the application of straightforward entitlements. In some cases, international law neither supplies specific rules nor entitles one side or the other to resolve the issue unilaterally, thus leaving the parties with only the organizing principles of sovereign equality and joint stewardship as guides. This explains why some territorial disputes qualify for mandatory multilateralism: states can claim territorial jurisdiction backed by property-like rules only after negotiation or third-party dispute resolution because unilateral action by either side would constitute a wrongful usurpation of joint international lawmaking power. A usurpation of this kind would violate sovereign equality by arrogating to one party a prerogative not held by another, and it would infringe joint stewardship because it would deny the equal lawmaking capacity implicit to joint stewardship. Sovereign equality and joint stewardship also explain why disputes involving conflicting legal entitlements are subject to mandatory multilateralism under international law. When two states seek to exercise their rights or powers in conflicting ways or hold overlapping entitlements to the same shared resource, neither is in a position to exercise their own rights without wrongfully interfering with the other's rights. A state that asserted the prerogative to act unilaterally under these circumstances would subject the other state to domination even if it never exercised the asserted prerogative.

International law's solution to this dilemma is mandatory multilateralism: states must negotiate or submit to third-party dispute resolution. This duty to cooperate in pursuing multilateral solutions to conflicts of international entitlements “constitutes a special application of a principle which underlies all international relations”—the principle of sovereign equality.Footnote ¹⁷⁷ And, in some cases such as Lac Lanoux, the injunction against unilateralism means that even when it is just one state alone exercising sovereign rights, the state is not entitled to do as it pleases but rather is legally required to take account of the legitimate interests of extraterritorial foreign nationals affected by its action.

In other contexts, mandatory multilateralism emanates from the principle of joint stewardship because particular international regimes commit rights or powers to the entire international community. Hence, multilateralism is mandatory for common resources,Footnote ¹⁷⁸ the UN Charter's collective security regime, the promotion of international human rights, and the enforcement of international criminal law, because each of these regimes is premised on the international community's joint stewardship over global public goods, which are matters of legitimate concern to all humanity. International law thus requires multilateral cooperation whenever unilateral state action would compromise sovereign equality or joint trusteeship by subjecting states to wrongful interference or domination.

The Substantive Dimension: Equitable Balancing

Mandatory multilateralism demands, first, that states accord due regard to the rights of other states and the international community by seeking an equitable balance among the relevant legal interests. Within the domain of mandatory multilateralism, states must pursue “an objectively positive interaction with another [state]’s interests and with those of the international community,”Footnote ¹⁸⁴ for the purpose “of reconciling them in as equitable a manner as possible.”Footnote ¹⁸⁵ To satisfy this obligation, each state must “take into consideration the various interests involved, … seek to give [other states] every satisfaction compatible with the pursuit of its own interests, and … show that it is genuinely concerned to reconcile the interests of the other … State with its own.”Footnote ¹⁸⁶

The duty of due regard finds clearest expression in international maritime law, where it has been codified in UNCLOS and other agreements.Footnote ¹⁸⁷ In the Fisheries Jurisdiction Cases, the ICJ invoked the duty of due regard as the primary basis for rejecting Iceland's assertion that the state's preferential fishing rights within its coastal waters would justify the wholesale exclusion of fishing vessels from other states.Footnote ¹⁸⁸ Emphasizing Iceland's legal obligation to accord due “regard to the position” of other interested states,Footnote ¹⁸⁹ the Court held that Iceland must “bring[] about an equitable apportionment of the fishing resources based on the facts of the particular situation, and having regard to the interests of other States which have established fishing rights in the area.”Footnote ¹⁹⁰ This inquiry was “not a matter of finding simply an equitable solution, but an equitable solution derived from the applicable law” and therefore sensitive to the “preferential” character of Iceland's fishing rights under international law.Footnote ¹⁹¹

An international tribunal likewise affirmed the duty of due regard's context-sensitive character in the Chagos Marine Protected Area Arbitration (Mauritius v. United Kingdom).Footnote ¹⁹² In its submissions to the tribunal, Mauritius challenged the United Kingdom's unilateral declaration of a marine protected area (MPA) around the Chagos Archipelago. Mandatory multilateralism applied to this declaration, in Mauritius's view, because the proposed MPA would impact Mauritius's legal rights as a coastal state.Footnote ¹⁹³ Accordingly, Mauritius asserted that the United Kingdom was obligated under UNCLOS to accord “due regard” to Mauritius's interests as a neighboring coastal state.Footnote ¹⁹⁴ The tribunal endorsed this argument, observing that “‘due regard’ calls for [a state] to have such regard for the rights of [another] as is called for by the circumstances and by the nature of those rights.”Footnote ¹⁹⁵ This duty

The tribunal thus underscored that due regard requires a context-sensitive balancing of the equities of a given case, taking into account the nature and importance of the relevant legal interests.

The WTO also has applied equitable balancing within mandatory multilateralism's domain. In the Shrimp/Turtle Dispute, the WTO addressed a potential conflict between two legal entitlements under the 1994 General Agreement on Tariffs and Trade: the United States’ legal right to take measures to conserve and protect natural resources, and other WTO members’ right to nondiscriminatory market access. Rather than allow one side to trump or veto the other, the WTO's Appellate Body concluded that the parties must maintain an

This equitable balancing was necessary, according to the Appellate Body, to accord due regard to the legal interests of all WTO members, thus affirming their sovereign equality by prohibiting either side from dominating or otherwise imposing inequitable terms on the other.

Equitable balancing applies equally to other contexts within the domain of mandatory multilateralism.Footnote ¹⁹⁸ Under international law, disputes over land and maritime borders invite equitable balancing.Footnote ¹⁹⁹ Equitable principles likewise apply to states’ joint stewardship of common resources, as reflected, for example, in the principle of “common but differentiated responsibilities” in international climate law.Footnote ²⁰⁰ Increasingly, states also accept that they must use equitable principles to address rivalrous claims to international watercourses and other shared resources.Footnote ²⁰¹ Equitable balancing does not appear expressly in international law governing the last two categories of mandatory multilateralism—threats to international peace and security and serious breaches of international human rights and international criminal law—but it is arguably implicit in norms such as the customary jus ad bellum requirement of proportionality.Footnote ²⁰² Across all of these contexts, international law requires states to use equitable criteria for the purpose of achieving an equitable result.Footnote ²⁰³

In short, the primary purpose of mandatory multilateralism's substantive dimension is to safeguard sovereign equality and joint stewardship. As Robert Kolb has observed, when states apply equitable balancing in good faith, it “inhibits the capacity of a subject to draw advantages [from] non-loyal and incorrect conduct infringing reciprocity and equality” (reinforcing sovereign equality) and “protects certain common interests against attacks by excessively individualistic [state] claims and pretentions” (reinforcing joint stewardship).Footnote ²⁰⁴ By requiring states to exercise their rights in a manner that reflects due regard for other states’ interests and collective interests of the international community, mandatory multilateralism “tempers individualistic voluntarism” in a manner that affirms sovereign equality and joint stewardship.Footnote ²⁰⁵

The Procedural Dimension

Mandatory multilateralism also imposes procedural duties of investigation, consultation, negotiation, and third-party dispute resolution.

Investigation

Mandatory multilateralism's first procedural requirement is the duty to investigate diligently how a state's laws, policies, and practices may impact the legal interests of other states and collective interests of the international community. Without such an investigation, the substantive duty of due regard would be practically meaningless; a state could not evaluate the equities of a particular controversy effectively without first making a good faith effort to identify and evaluate all of the relevant legal interests.

The duty of diligent investigation finds clearest expression in the ICJ's Fisheries Jurisdiction Cases.Footnote ²⁰⁶ In a pivotal passage, the ICJ explains how international maritime law has transitioned, in Wolfgang Friedmann's words, from a “law of co-existence” to a “law of co-operation”:Footnote ²⁰⁷

Although this passage focuses on customary norms of international maritime law, the Court's observations have broader applications to mandatory multilateralism writ large. To satisfy their general duty of due regard, states must take initiative to find equitable solutions that respect the applicable law and are based on the best available evidence. This requirement to undertake a diligent investigation is necessary to ensure that a state's laws, policies, and practices respect the principles of sovereign equality and joint stewardship.Footnote ²⁰⁹ Diligent investigation is therefore an essential component of the new international law of co-operation.

Consultation

In the passage excerpted above from the Fisheries Jurisdiction Cases, the ICJ also asserts that under customary international law states must “keep under review” and “examine together” how to equitably balance their respective interests and the collective interests of the international community.Footnote ²¹⁰ This suggests a second procedural requirement: when operating within mandatory multilateralism's domain, states must consult with one another, exchanging relevant information in a spirit of cooperation. Other international tribunals have confirmed that this duty to consult arises when states assert conflicting rights under international law,Footnote ²¹¹ and many treaties require states to exchange information and pursue cooperative dialogue regarding matters within mandatory multilateralism's domain.Footnote ²¹² These deliberative requirements affirm sovereign equality and joint stewardship by ensuring that states are able to make informed decisions regarding matters that may affect their rights and the collective interests of the international community.

Negotiation

When states disagree about the best way to achieve an equitable solution within mandatory multilateralism's domain, they are legally obligated to pursue peaceful dispute-resolution via negotiation. Good faith negotiation honors the principles of sovereign equality and joint stewardship by ensuring that all interested parties can participate meaningfully and have their legitimate interests taken into account.

The ICJ has been afforded many opportunities to clarify what the duty of good faith negotiation entails. Some of these cases have involved treaties that expressly require states to endeavor to resolve disputes through negotiation before resorting to adjudication.Footnote ²¹³ In other cases, however, the ICJ has held that a duty of good faith negotiation applies to matters within mandatory multilateralism's domain even in the absence of a specific treaty-based requirement because this reflects “a special application of a principle which underlies all international relations.”Footnote ²¹⁴ As we explained in Part III, the organizing principles that underlie the duty of good faith negotiation in these contexts are sovereign equality and joint stewardship.

The duty of good faith negotiation has several salient features that apply across all of the diverse contexts where it arises. First, it demands initiative and sustained commitment.Footnote ²¹⁵ As international courts and tribunals have explained, good faith negotiation “entail[s] more than the plain opposition of legal views or interests between two parties, or the existence of a series of accusations and rebuttals, or even the exchange of claims and directly opposed counter-claims.”Footnote ²¹⁶ Negotiations must be “meaningful” in the sense that each side demonstrates a willingness to pursue agreement, not merely to go through the motions.Footnote ²¹⁷ Good faith negotiation also requires openness to “compromise, even if that mean[s] the relinquishment of strongly held positions earlier taken. It implies a willingness for the purpose of negotiation to abandon earlier positions and to meet the other side part way.”Footnote ²¹⁸ Hence, the idea that one side would “insist upon the complete capitulation of the other side” is “inconsistent with … ‘negotiation.’”Footnote ²¹⁹ The duty to negotiate in good faith also entails a duty of due diligence.Footnote ²²⁰ States must undertake a “persevering quest for an acceptable compromise,”Footnote ²²¹ demonstrating that they are “internally concerned with balancing the [relevant] rights and interests,” rather than simply going through the motions.Footnote ²²²

In the end, however, mandatory multilateralism's requirement of good faith negotiation does not obligate states to actually conclude an agreement resolving their disputes.Footnote ²²³ Sometimes states disagree in perfectly good faith about the terms of an equitable solution. To require states to accept an agreement that they genuinely believe is inequitable would subject them to the unilateral will of the other side, which is inconsistent with sovereign equality and joint stewardship. Accordingly, mandatory multilateralism does not require states to actually conclude international agreements, provided they persevere in pursuing an equitable resolution in good faith.Footnote ²²⁴

International courts and tribunals are typically reluctant to find bad faith absent “clear and convincing evidence” that a state seeks “to prevent any reasonable agreement.”Footnote ²²⁵ Bad faith might be established if a state arbitrarily breaks off or delays negotiations, declines to follow established procedures for negotiation, or refuses to consider counter-proposals or relevant equitable considerations.Footnote ²²⁶ Under any of these circumstances, a state's intransigent behavior would reflect unilateralism through covert means, which in turn would infringe sovereign equality and joint stewardship.

Third-Party Dispute Resolution

When multilateral cooperation is mandatory under international law, a negotiated agreement is the preferred solution for several reasons. First, as compared to international courts and tribunals, states have superior access to the kinds of information and expertise that would be necessary to determine an equitable solution to international disputes.Footnote ²²⁷ Second, when states resolve disputes through negotiated compromise, the choices they make together plausibly reflect exercises of collective self-determination. Third, it stands to reason that states will be more likely to accept a solution as equitable if they have participated in and consented to the solution. Consequently, international courts and tribunals usually give states every opportunity to conclude agreements resolving issues within mandatory multilateralism's domain.Footnote ²²⁸

If states are unable to resolve disputes regulated by mandatory multilateralism, they must pursue mediation, arbitration, adjudication, or some other form of third-party dispute resolution. Support for this principle can be found in Article 33 of the UN Charter, which charges states with resolving their disputes through peaceful means.Footnote ²²⁹ The General Assembly's Friendly Relations Declaration likewise describes the pursuit of peaceful third-party dispute resolution as an obligation incumbent upon all states.Footnote ²³⁰ Third-party dispute resolution promotes sovereign equality and joint stewardship by ensuring that states do not appoint themselves judge and party to the same cause.

Under international law today, states cannot compel one another to accept any particular forum for third-party dispute resolution without their consent; the choice of a particular forum for third-party dispute resolution must be the product of consensus between the relevant parties.Footnote ²³¹ Once states agree on a particular mechanism and venue for third-party dispute resolution, however, they assume a concomitant duty to follow through in good faith.Footnote ²³²

Managing Entrenched Disputes

States sometimes encounter serious roadblocks in their efforts to resolve their disputes through negotiation or third-party dispute resolution. Entrenched disputes between states are not always the product of bad faith. States may disagree in good faith about the ingredients of an equitable solution to their dispute, and they may fail to reach consensus on a mechanism for resolving the dispute (e.g., mediation, arbitration, adjudication) or on the specific institution to assist them in this process (e.g., ICJ, PCA, regional courts). As Monica Hakimi has shown, multilateral engagement sometimes illuminates points of disagreement between states, sparking new conflicts and intensifying old ones.Footnote ²³³ As long as such disagreements remain unresolved, international controversies can drag on without the expectation of an immediate resolution.

The Gabčikovo-Nagymaros Case offers a classic example of entrenched disagreement.Footnote ²³⁴ In 1993, Hungary and Slovakia sought the ICJ's assistance in resolving a dispute over Hungary's unilateral suspension of a joint-venture between the two countries to develop a system of locks and hydroelectric power plants on the Danube River.Footnote ²³⁵ Hungary argued that the project negatively impacted its legal interest and the international community's collective interest in preserving the river's ecological health.Footnote ²³⁶ Slovakia contended, in turn, that Hungary's actions violated a treaty between the two countries.Footnote ²³⁷ After concluding that both parties had violated their international legal obligations, the ICJ sent the dispute back to the parties with the instruction to “find an agreed solution” through “good faith” negotiation.Footnote ²³⁸ For nearly two decades, however, the two sides made little progress in negotiations, raising the specter of perpetual deadlock.Footnote ²³⁹

International law responds to entrenched disputes like the Gabčikovo-Nagymaros Case by imposing special requirements of mandatory multilateralism. First, states must continue to pursue new dispute resolution mechanisms in good faith until they find a successful avenue for achieving an equitable resolution.Footnote ²⁴⁰ Second, although states may take provisional steps to secure their legal interests once it becomes clear that an impasse has been reached,Footnote ²⁴¹ they must notify other interested parties of such measures,Footnote ²⁴² maintain a continuous process of dialogue to ensure that their provisional measures do not foreclose a multilateral solution,Footnote ²⁴³ and avoid any actions that would “establish a fait accompli capable of prejudicing the outcome of negotiations.”Footnote ²⁴⁴ The last requirement is especially critical: to respect the principles of sovereign equality and joint stewardship, states must refrain from taking any actions unilaterally that would cause permanent and irreversible harm to other states’ interests and collective interests of the international community.Footnote ²⁴⁵ In particular, they must avoid measures that might so aggravate international tensions as to imperil international peace and security.Footnote ²⁴⁶ Each of these requirements are necessary to reconcile sovereign equality and joint stewardship with the often-slow pace of international dispute resolution.

The various substantive and procedural requirements of mandatory multilateralism share a common logic. What unites these requirements is the idea that states under international law are formal equals and joint stewards of the international community's collective interests. International law does not obligate states to pursue common purposes across all fields and topics. But when cooperation is necessary because an important and transnational public good is at stake, international law does require states to pursue solutions that reflect sovereign equality and joint stewardship by giving due regard to other states’ legal interests. This means that states must engage one another in an inclusive decision-making process that aims to achieve an equitable result.

Objections to Mandatory Multilateralism

The requirements entailed by mandatory multilateralism have attracted their share of critics. Some object that these requirements are question-beggingFootnote ²⁴⁷ and “singularly unhelpful”Footnote ²⁴⁸ because they are too indeterminate to resolve international disputes. Broad substantive standards like “good faith,” “due regard,” and “equitable balancing” might provide general guideposts for negotiations, but they rarely dictate specific outcomes.Footnote ²⁴⁹ Likewise, procedural duties to negotiate cannot bear fruit if states cannot find common ground. The requirement to pursue third-party dispute resolution, in particular, has been criticized as “essentially circular, since if the parties are not agreed on reference to arbitration or judicial settlement the process of negotiation goes around and around, potentially without end.”Footnote ²⁵⁰ Is mandatory multilateralism therefore an exercise in futility?

Generally speaking, we think not. Although equitable balancing may lack the precision of bright-line rules, it is not devoid of content. Nor is international negotiation based on equitable balancing destined to fail. In many settings, states have strong incentives to resolve their disputes peacefully, and mandatory multilateralism's substantive and procedural requirements can help to channel negotiations in a direction that brings the parties closer to agreement.Footnote ²⁵¹ Even when states are unable to resolve their disputes expeditiously—as was the case in both the Gabčikovo-Nagymaros Case and the Shrimp/Turtle Dispute—mandatory multilateralism's requirement that states maintain a continuous dialogue may bolster the chances that a consensus-based solution will eventually emerge.Footnote ²⁵² In the meantime, mandatory multilateralism disciplines negotiations by prohibiting some (injurious and irreversible) provisional measures and taking some proposals for (manifestly inequitable) solutions off the negotiation table.Footnote ²⁵³ If states attempt to bypass the requirements of mandatory multilateralism, international courts and tribunals can, and routinely do, bring them back into line, notwithstanding that such courts rely on state consent to acquire jurisdiction.

A more serious objection to mandatory multilateralism is that in practice it sometimes undermines sovereign equality and joint stewardship. During negotiations, powerful states may find that they can compel weaker states to accept disadvantageous deals that cement relationships of domination. In some contexts, even the requirement that states pursue an equitable result may be used to disproportionately benefit the powerful. Valentina Okaur-Bisant has observed, for example, that applying equitable principles to the apportionment of international rivers tends to “reward the countries … that are first in time to develop a shared river,” thereby systematically disadvantaging poorer countries that are behind the development curve.Footnote ²⁵⁴ This observation underscores the risk that powerful states may exploit negotiation as a “hegemonic tool”Footnote ²⁵⁵ for dominating weaker states, thereby undermining sovereign equality and joint stewardship.

We readily acknowledge the force of this critique: like other institutions and norms of international law, mandatory multilateralism is vulnerable to abuse in the hands of powerful states.Footnote ²⁵⁶ We doubt, however, that mandatory multilateralism is more susceptible to abuse than the alternative. When mandatory multilateralism applies, it offers weaker states formal legal protections that they can assert to counter great power domination. Although mandatory multilateralism denies weaker states the right to veto powerful states’ preferred solutions, the other side of the coin is that powerful states also may not lawfully impose their preferred solutions on weaker states unilaterally. Hence, if weaker states hold out for a more equitable deal, powerful states have three choices under international law: (1) they may offer to sweeten the deal; (2) they may declare a stalemate and impose (impermanent and reversible) provisional measures while continuing to pursue international dialogue; or (3) they may submit the dispute to a third-party for decision in accord with equitable principles. This limited menu of options gives weaker states leverage they can use to counteract, however imperfectly, powerful states’ asymmetric bargaining position in international negotiations. Outside the domain of mandatory multilateralism, weaker states have no such protections.

Navigating Territorial Disputes: The South China Sea

The South China Sea has been a locus of conflict for centuries. The struggle has intensified over the past several decades, as populations in the region have swelled, fisheries have dwindled, and technological innovation has opened the door to offshore drilling. Brunei, China, Malaysia, the Philippines, Taiwan, and Vietnam have each laid claim to parts of the South China Sea by establishing outposts on diminutive islands, reefs, and shoals.Footnote ²⁵⁸ Among these states, China has taken the most aggressive stance, arguing that virtually the entire Sea falls within its sovereign jurisdiction, including the Macclesfield Bank, Paracel Islands, Pratas Islands, Scarborough Shoal, and Spratly Islands, with their adjacent waters.Footnote ²⁵⁹ To reinforce these claims, China has constructed dozens of “island fortresses” in the South China Sea—in some cases building up shallow reefs and shoals to support naval ports, weapons systems, and even entire airstrips.Footnote ²⁶⁰ Other states have vigorously contested China's expansive claims.Footnote ²⁶¹

In 2006, the Philippines initiated an arbitration against China under UNCLOS, seeking a determination that various maritime features claimed by China were insufficient to support EEZs and other maritime rights under international law.Footnote ²⁶² When the tribunal rejected China's objections to jurisdiction,Footnote ²⁶³ China refused to participate further in the proceeding.Footnote ²⁶⁴ The tribunal ultimately issued an award on the merits endorsing the Philippines’ central arguments.Footnote ²⁶⁵ China, however, declared this award “null and void” with “no binding effect on China,”Footnote ²⁶⁶ and it stepped up its own naval exercises and construction of artificial islands throughout the region.Footnote ²⁶⁷ In response, the United States and some other countries have conducted periodic “freedom of navigation” exercises in the South China Sea in pointed defiance of China's pretentions to sovereignty.Footnote ²⁶⁸ Tensions in the region thus continue to run high.Footnote ²⁶⁹

Mandatory multilateralism has a variety of important applications to the South China Sea dispute. First, any maritime rights that states assert against one another must be anchored in multilateral legal norms, i.e., international treaties, customary international law, or general state practice. States may not rest their claims to the South China Sea on their own unilateral historical practices (no matter how longstanding), national laws (no matter how just), or preferred reformulation of international norms (no matter how desirable). Accordingly, China may not claim maritime zones in the South China Sea based solely on its people's historic fishing practices or the fact that it has unilaterally asserted jurisdiction over the Sea in the past.Footnote ²⁷⁰ Such considerations are insufficient to establish sovereignty under international maritime law.Footnote ²⁷¹ Nor may China and its neighbors claim EEZs in the South China Sea based on rocks, artificial islands, or other features that do not qualify for EEZs under international maritime law.Footnote ²⁷² To the extent that gaps in UNCLOS might leave some key issues unresolved, China cannot simply fill the gaps unilaterally with its own preferred views. Instead, it must engage with other states to develop new treaty-based or customary norms that reflect due regard for the relevant legal interests of other states and the international community. The same legal constraints apply equally to other states in the region.

Second, states must comply with mandatory multilateralism's procedural requirements of investigation, consultation, and good faith negotiation or third-party dispute resolution. For several years, the Association of Southeast Asian Nations (ASEAN) has convened its members to consult and negotiate with China for the purpose of brokering a consensus-based “code of conduct” for the South China Sea.Footnote ²⁷³ Although these negotiations are still ongoing, the draft code that is currently under consideration achieves only modest results. Critics have observed that the draft purports to be nonbinding, lacks a dispute-resolution mechanism, and—most importantly—does not establish norms or procedures to resolve the central questions of maritime delimitation that have divided the region.Footnote ²⁷⁴ This appears to be by design: China has worked behind the scenes to minimize and stall multilateral engagement to ensure that its militarization of the South China Sea eventually renders its claims to sovereignty a fait accompli.Footnote ²⁷⁵

Such tactics are inconsistent with international maritime law's commitment to multilateralism. At a minimum, mandatory multilateralism dictates that China must respect the rights that other states in the region have under UNCLOS to claim jurisdiction over various maritime zones adjacent to their land territory and islands in the South China Sea. To the extent that respect for others’ rights raises unresolved questions of maritime delimitation, China must take these questions to the negotiation table or to third-party dispute resolution rather than proceed unilaterally. Although mandatory multilateralism does not preclude hard-nosed negotiation, it does require states to negotiate in good faith, manifesting “a willingness for the purpose of negotiation to abandon earlier positions and to meet the other side part way.”Footnote ²⁷⁶ The idea that one of the parties would “insist upon the complete capitulation of the other side” is “inconsistent with … ‘negotiation.’”Footnote ²⁷⁷ Instead, international law requires a good faith effort to reach common ground based on multilateral norms. And if negotiation stalls, China must cooperate in good faith to find a mutually acceptable mechanism for third-party dispute resolution.

Third, as long as the South China Sea dispute drags on, states must refrain from taking steps that would irreversibly alter the status quo.Footnote ²⁷⁸ This means that they must suspend construction in disputed, environmentally sensitive areas pending the outcome of international negotiations or third-party dispute resolution.Footnote ²⁷⁹ They must also avoid actions that could undermine international peace and security in the region, including the threat or use of force against foreign vessels traveling peacefully through contested waters.Footnote ²⁸⁰ Respect for these requirements is essential to honor the principle of sovereignty equality, which China has celebrated as “crucial for the stability of international relations.”Footnote ²⁸¹

China's actions persistently contravene the norms of mandatory multilateralism. Recalcitrance on the part of China, however, does not imply that the legal obligations of mandatory multilateralism are not really obligations or not really legal, or that the South China Sea controversy is inherently unsuited to their application. Rather, it confirms the findings of the arbitral tribunal that China's behavior is unlawful. The most that can be reasonably expected of an international legal framework is that it treats the parties within it equitably and recognizes justice claims grounded in law. The fact that there is no supranational coercive authority capable of compelling China to comply with international law is no more a knock against mandatory multilateralism than it is against the many other areas of international law that lack coercive executive power, such as human rights law, refugee law, trade law, labor law, and environmental law.

Administering Common Resources: Climate Change

In 2015, representatives from 196 states met near Paris to negotiate and draft an agreement that would address climate change at the global level.Footnote ²⁸² These talks ultimately produced the Paris Agreement.Footnote ²⁸³ As of January 2019, 195 UNFCCC members (194 states and the European Union) have signed the Agreement, and 184 have become parties to it.Footnote ²⁸⁴ Its principal aim is to promote the adoption of policies that will reduce greenhouse gas emissions, thereby “[h]olding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels.”Footnote ²⁸⁵ A further objective is “[i]ncreasing the ability to adapt to the adverse impacts of climate change and foster climate resilience and low greenhouse gas emissions development.”Footnote ²⁸⁶ As the chief means of attaining these goals, the Agreement envisions all countries developing and continually updating “nationally determined contributions” (NDCs) to mitigate climate change.Footnote ²⁸⁷ NDCs are to be submitted to the United Nations every five years and then used to assess state parties’ compliance with their ongoing commitments, as we explain further below.Footnote ²⁸⁸ Sensitive to the concerns of developing countries, the preamble affirms the principle of “equity and common but differentiated responsibilities and respective capabilities.”Footnote ²⁸⁹ More concretely, the Paris Agreement provides a framework for preexisting commitments of $100 billion a year in climate finance for developing countries by 2020, and for further financial assistance subsequently.Footnote ²⁹⁰ Although the plan's success will depend on the willingness of countries to follow through on these commitments and to develop and adhere to meaningful NDCs, we have suggested in previous writing that the obligation of states to do so is explained by the idea that states, severally and jointly, are fiduciaries of humanity.Footnote ²⁹¹

We now consider the ways the legal regime established by the Paris Agreement reflects the norms of mandatory multilateralism, and then assess from this perspective the present U.S. administration's stated intention to withdraw from the Agreement. The UNFCCC and the Paris Agreement both acknowledge that mitigating climate change and its adverse effects is “a common concern of humankind.”Footnote ²⁹² Although the Paris Agreement is careful to protect developing countries with the principle of “common but differentiated responsibilities,”Footnote ²⁹³ all state parties are expected to participate in the Agreement's regime of international cooperation. Notably, however, whereas the Kyoto Protocol established legally binding emission-reduction targets for developed countries,Footnote ²⁹⁴ the Paris Agreement does not. Instead, the Paris Agreement requires all states to develop NDCs, either by themselves or jointly with others, including through the use of “internationally transferred mitigation outcomes” (typically, a developed country would finance realization of a developing country's NDC).Footnote ²⁹⁵ The Agreement calls for each party's successive NDC to “represent a progression beyond” the prior NDC.Footnote ²⁹⁶ State parties are likewise legally required to submit their NDCs to the United Nations and a public registry, report on progress every two years, and have their progress reports reviewed by technical experts and peers.Footnote ²⁹⁷ The Agreement further envisions a “global stocktake” every five years to assess collective progress toward its objectives, with the first stocktake scheduled for 2023.Footnote ²⁹⁸

The Paris Agreement seeks to strike a balance that takes into account state autonomy and self-determination, on the one hand, and the urgent need for a global response to climate change, on the other. State autonomy is respected through the use of NDCs that states are legally entitled to design and implement as they wish. The demands of climate change are reflected in the legal requirement on states to establish, implement, and report periodically on progress toward their NDCs. This activity is wedded to the annual Conference of Parties meetings under the UNFCCC framework. In this context, states retain an overarching obligation from the UNFCCC to “protect the climate system for the benefit of present and future generations of humankind,”Footnote ²⁹⁹ and to do so cooperatively, such as through the negotiated use of “internationally transferred mitigation outcomes.”Footnote ³⁰⁰ Thus, explicitly and implicitly, the UNFCCC and the Paris Agreement require states to negotiate with one another in good faith, and on an ongoing basis, for the purpose of developing and implementing NDCs capable of achieving collectively the goals of the Paris Agreement. In the event of a dispute concerning the interpretation or application of the UNFCCC or the Paris Agreement, the controversy is remitted to the ICJ, arbitration, or conciliation.Footnote ³⁰¹ The Paris Agreement thus embraces a form of mandatory multilateralism akin to the form established under UNCLOS, where contending parties are obligated to negotiate in good faith, resorting to third-party dispute resolution only if necessary.

The principle of sovereign equality is respected under the Paris Agreement because no state is entitled to dictate terms to another, and every state is ultimately responsible for the content of its NDC. The principle of joint stewardship is put into action by the Paris Agreement's delegation to states of the responsibility to craft meaningful NDCs to reduce greenhouse gas emissions and address the adverse effects of climate change. Joint stewardship assumes an institutional form by the Paris Agreement's use of the annual UNFCCC Conference of Parties to which every member belongs and has one vote, allowing the Conference to speak collectively on behalf of all.Footnote ³⁰²

Arguably, the international community has elected to place climate change policy under joint stewardship precisely because the reduction and mitigation of atmospheric pollution poses a serious collective action problem. Self-interested states would prefer to free ride, letting others bear the cost of mitigation measures, while they themselves avoid those costs while benefitting from a relatively healthy environment. The logic of the prisoner's dilemma encourages states to pursue their narrow self-interest, since whether or not other states shoulder the burden of climate mitigation, a state will typically do better economically by avoiding the burden. But, of course, if a plurality of heavily polluting states adopted this policy, climate mitigation would be severely threatened if not doomed. The mandatory multilateralism of the Paris Agreement addresses this collective action problem by providing a framework for joint stewardship that makes the development and implementation of NDCs transparent, with the hope that national policymakers may be held accountable. Of course, this approach depends on policymakers caring about climate change and the Agreement's multilateral process.

The present U.S. administration has indicated that, as part of its “America First” policy, the United States will be withdrawing from the Paris Agreement.Footnote ³⁰³ Article 28 of the Agreement provides that a party may give notice of withdrawal “any time after three years from the date on which [the] Agreement has entered into force” for that party, but the withdrawal takes effect only one year after notification.Footnote ³⁰⁴ Withdrawal would make the United States a free rider on the mitigation efforts of others and would constitute a brazen assertion of unilateralism. The assertion would be brazen because, as noted, the Paris Agreement does not subject state parties to emission-reduction quotas or targets. States must merely develop some climate change mitigation policy in non-binding (but good faith) negotiations with others, and be willing to subject the policy's implementation to public review. Withdrawal from the Paris Agreement would be an outright rejection by the United States of international legal norms of mandatory multilateralism in the field of climate change. It would also constitute a serious impediment to collective action on the environment, in part because the United States is one of the world's largest carbon emitters, and in part because defections from collective action regimes and open free riding tend to breed resentment and further defections.

More significantly, however, it is arguable that in this context the substantive and procedural norms of mandatory multilateralism are binding independently of their codification in the Paris Agreement. The rationale for the theory proceeds from the premise that because states’ carbon emissions spill over into the global atmosphere possessed in common by all, the only practical way to safeguard sovereign equality and avoid unilateralism is to charge states as co-equals with joint stewardship of the atmosphere. For this charge to be legally meaningful, states must have some obligation to take it seriously. The legal obligation to cooperate with other states in addressing the harmful effects of climate change derives from the issue's recognized status under the UNFCCC, which is (arguably) evidence of a customary rule that states have an obligation to mitigate climate change because the environment is a “common concern of humankind.”Footnote ³⁰⁵ Mandatory multilateralism in this context would require the United States to respect the object and purpose of the Paris Agreement by taking good faith steps to mitigate climate change. The United States would enjoy wide discretion to design and implement mitigation measures, much as state parties to the Paris Agreement enjoy broad authority over the development and implementation of NDCs. The United States would also, however, be under an obligation to exercise that discretion in a way that did not subvert the collective mitigation efforts of other states, and in a manner that demonstrated due regard for other states touched by its greenhouse gases. In addition, mandatory multilateralism would entail procedural obligations of investigation, consultation, negotiation, and third-party dispute resolution. Thus, even if the United States completes its withdrawal from the Paris Agreement, it may still be bound by substantive and procedural customary norms of mandatory multilateralism that call on the United States to have due regard for the environmental interests of other states.

This again raises the question of compliance. What if the United States withdraws and explicitly refuses to recognize the validity or applicability of any international legal obligations in this sphere? Such a move could have far-reaching, and potentially disastrous consequences for global efforts to combat climate change. Purely as a conceptual matter, however, the compliance problem does not appear any more or less pressing here than in other areas of international law. Moreover, issues of compliance go to the motivation of states to comply with international norms and the likelihood of their compliance with them, whereas our project has been to theorize norms that are already part of international legal practice. While practical concerns counsel publicists to take compliance seriously, elaborating the nature and implications of legal principles, as we have tried to do, is a separate inquiry.

A further issue raised by the prospect of customary norms of mandatory multilateralism concerns whether the persistent objector doctrine would apply, such that unwilling states can legally opt out of multilateral regimes. In our view, these states would be in the same legal position as states that attempt to negotiate a settlement of a dispute in good faith, but simply cannot reach amenable terms with the counterparty. Like these states, persistent objectors would remain subject to norms that prohibit them from adopting measures or positions that undermine the efforts of other states to develop an equitable multilateral framework. And they would remain subject to the obligation to continue to pursue good faith efforts to reach a mutually acceptable outcome. We admit that, as a general matter, holding states to a customary obligation to seek third-party dispute resolution is, at this point in the evolution of international law, more prescription than description. However, it is nonetheless a prescription wholly consonant with the principles of sovereign equality and joint stewardship that underlie mandatory multilateralism's other norms.

Accommodating Landlocked States: The Dispute Between Bolivia and Chile

Mandatory multilateralism also clarifies the legal position of landlocked states—a classic case of conflicting entitlements under international law. Article 125 of UNCLOS provides that landlocked states are entitled to “the right of access to and from the sea”—including “transit through the territory of transit States by all means of transport”—so that they can enjoy the full range of rights associated with “the freedom of the high seas and the common heritage of mankind.”Footnote ³⁰⁶ Article 125 also recognizes, however, that these rights are in tension with transit states’ “full sovereignty over their territory.”Footnote ³⁰⁷ Accordingly, Article 125 provides that transit states “have the right to take all measures necessary to ensure that the rights and facilities provided … for land-locked States shall in no way infringe their legitimate interests.”Footnote ³⁰⁸ How does UNCLOS reconcile the resulting conflict between transit states’ territorial sovereignty and landlocked states’ right to access the seas? The solution contemplated is mandatory multilateralism. Article 125 provides: “The terms and modalities for exercising freedom of transit shall be agreed between the land-locked States and transit States concerned through, bilateral, subregional or regional agreements.”Footnote ³⁰⁹ Thus, UNCLOS recognizes that the legal entitlements of landlocked states and transit states can be harmoniously reconciled only through multilateral decision making.

Our account of mandatory multilateralism further illuminates the legal obligations enshrined in Article 125. It suggests that Article 125 is best read as obligating transit states to cooperate in good faith with landlocked states to determine the “terms and modalities for exercising freedom of transit.” To satisfy this obligation, transit states must investigate and consult with landlocked states to fully understand and accommodate their legitimate interests. Transit states may not arbitrarily withhold—or threaten to withhold—safe passage through their territory. Landlocked states, in turn, must respect transit states’ territorial integrity and political independence by accepting reasonable constraints on their passage through transit states. Article 125 thus places landlocked states and transit states under mutual obligations to establish cooperative and multilateral frameworks for facilitating oceanic access. Failure to reach agreement about specific “terms and modalities” is not necessarily a violation of Article 125, as long as the parties remain committed to, and actively engaged in, the pursuit of an equitable solution. If negotiations reach an impasse, mandatory multilateralism complements Article 125 by dictating that both sides must pursue third-party dispute resolution.

A long-running dispute between Bolivia and Chile illustrates both the limits and promise of mandatory multilateralism with regard to conflicts between landlocked and transit states. The dispute arises out of events that transformed Bolivia into a landlocked state: Chile's forcible seizure and annexation of Bolivia's coastal territory in the late-nineteenth century.Footnote ³¹⁰ Following the seizure and annexation, Bolivia and Chile sought to normalize their relations through a series of agreements, and Bolivia continued to seek its own sovereign territorial outlet to the Pacific. In 1904, Bolivia and Chile concluded a Treaty of Peace and Friendship in which Bolivia formally recognized Chile's sovereignty over its former territory in exchange for financial compensation, but without expressly addressing Bolivia's desire for an independent corridor to the ocean.Footnote ³¹¹ Over the next century, Bolivia periodically renewed negotiations with Chile toward acquiring a corridor to the Pacific over which Bolivia would be sovereign, but without success. In 2013, Bolivia initiated proceedings in the ICJ, seeking to force Chile back to the negotiation table for the purpose of negotiating the surrender of a corridor to Bolivia.Footnote ³¹² Bolivia asserted that at various critical junctures in their diplomatic relations, Chile had undertaken a legal obligation to negotiate with Bolivia for the purpose of ending once and for all Bolivia's misfortunate status as a landlocked state.Footnote ³¹³ Chile, however, vigorously rejected the notion that it had undertaken any such legal duty to negotiate a land surrender. Although Chile acknowledged that it had entertained Bolivian invitations to negotiate on a number of occasions, it categorically rejected the suggestion that its conduct reflected an intention to undertake a legal duty to negotiate with Bolivia in the future over the possible transfer of Chilean territory to Bolivia.Footnote ³¹⁴

To be clear, in proceedings before the ICJ, Bolivia did not assert its right under Article 125 to negotiate transit rights to the Pacific with Chile. Instead, Bolivia set its sights on a more ambitious target: securing a judgment that it was legally entitled to negotiate with Chile concerning the possible acquisition of Chilean territory.Footnote ³¹⁵ Because the acquisition of foreign territory is not an issue that triggers mandatory multilateralism,Footnote ³¹⁶ the success of Bolivia's strategy depended on the ICJ agreeing that Chile had, in fact, voluntarily undertaken an independent obligation to negotiate with Bolivia for these purposes. Had Chile undertaken such an obligation, then it would have borne a relatively modest duty to receive and consider proposals from Bolivia in good faith.Footnote ³¹⁷ Chile would not, however, have been required to endorse or give any special weight to Bolivia's proposals. Unlike settings where mandatory multilateralism applies, triggering the more robust duty of due regard, Chile would have been free to decide for itself whether, or on what terms, it would agree to relinquish some of its coastal territory to Bolivia. Ultimately, however, the ICJ concluded in its judgment of October 1, 2018, that Chile had not voluntarily undertaken any such duty to negotiate with Bolivia for the purpose of granting Bolivia “sovereign access” to the Pacific.Footnote ³¹⁸

Chile bears more robust duties of cooperation when it comes to facilitating transit through its territory pursuant to Article 125. Because Bolivia's right to access the ocean under UNCLOS is in tension with Chile's right to territorial integrity, Article 125 requires the two states to reconcile their conflicting entitlements through multilateralism. Bolivia and Chile must therefore cooperate in investigating, consulting, negotiating, and, if necessary, pursuing third-party dispute resolution to establish equitable “terms and modalities” that balance their respective interests.Footnote ³¹⁹ In pursuing multilateral solutions, each state must respect the other's legitimate interests and manifest an openness to compromise.

In many respects, the relationship between Bolivia and Chile already reflects the successful implementation of these principles. Pursuant to the 1904 Treaty of Peace and Friendship, Chile has connected Bolivia to the Pacific by constructing and maintaining a railway line and a highway between Bolivia's capitol, La Paz, and the Chilean port city of Arica.Footnote ³²⁰ Chilean lawmakers have worked with Bolivia to reduce regulatory red tape that would otherwise impede the free flow of people and goods across Chilean territory.Footnote ³²¹ Bolivian cargo is exempt from Chilean taxes, and Chile allows Bolivia to exercise customs powers in Arica over cargo traveling to or from Bolivia.Footnote ³²² Pursuant to agreements negotiated in 1955 and 1957, a Bolivian state-owned company operates a pipeline from Sica in Bolivia to Arica, facilitating the shipment of Bolivian oil across the high seas to markets around the world.Footnote ³²³ To be sure, Bolivia clearly believes that further concessions by Chile are necessary—including a permanent transfer of coastal territory between the countries—to strengthen Bolivia's political independence and facilitate its economic development.Footnote ³²⁴ Yet, these lingering grievances should not overshadow the substantial progress that the states have made over time in reconciling their conflicting interests through multilateral engagement. For generations, Bolivia and Chile have managed to cooperate productively—investigating, consulting, and negotiating with one another on a wide variety of issues—in a good faith effort to balance equitably their respective sovereign interests. The fact that such a robust partnership has taken root and flourished—even as the two states remain bitterly divided over Bolivia's aspiration to acquire a territorial corridor to the Pacific—is a testament to the promise of mandatory multilateralism.Footnote ³²⁵