Twenty-five years ago, international courts (ICs) were few in number and, outside the supranational island of Europe, mostly backwaters, deciding only the handful of cases that states saw fit to litigate before them. Since the end of the Cold War, states have created a raft of new international economic, human rights, and criminal courts and granted many of these courts compulsory jurisdiction and access for non-state actors, resulting in a flood of new cases. In The New Terrain of International Law: Courts, Politics, Rights, Karen Alter provides the most ambitious, comprehensive, and successful analysis of this new world of international courts and the impact they have exerted on international and domestic law and politics. Painting on the broadest possible canvas, yet also in fine detail, Alter demonstrates convincingly that international courts have changed fundamentally in character as well as in number, and that they have altered international politics in ways that directly challenge national sovereignty and promote the rule of law.

Reflecting its subtitle, the book unfolds in three parts, dealing with courts, politics, and rights, respectively. The first section, on courts, is motivated by the empirical observation that the number and nature of ICs have changed since the end of the Cold War. Outside Europe, the few pre-1989 ICs were what Alter calls “old-style” courts, limited to resolving disputes among states that voluntarily consented to their jurisdiction. By contrast, the vast majority of post-1989 ICs are “new-style” courts, characterized by two key features: compulsory jurisdiction, and direct access to courts for non-state actors such as private litigants, international commissions, and international prosecutors—any of which can bring cases that states might once have blocked.

In support of these claims, Alter provides an extraordinarily rich analytical survey of the universe of 24 active ICs (Chapter 3). She chronicles the rise of new-style courts modelled largely on their pioneering European predecessors, mapping general trends as well as variations in court design, and their uneven distribution across three major subject areas (economics, human rights, and criminal law) and across space (with Latin America and Africa moving to embrace new-style courts even as most Asian and Middle Eastern countries remain aloof). She also demonstrates that the use of these courts has exploded, with all ICs issuing a total of 37,000 binding rulings, 91 percent since the fall of the Berlin Wall. Precisely because of this diffusion of European-style courts, Alter, herself a leading expert on the politics of the European Court of Justice, argues that that study of international law and courts must move “beyond the usual suspects” (p. 26) and the book does precisely this, providing detailed analyses of African, Latin American, Caribbean, and global courts.

Alter’s survey of courts is also revisionist in another sense, namely her insistence that ICs are not simply dispute-settlement bodies, but play some combination of four key roles: dispute settlement (among mutually consenting states); enforcement of international law (most effective, she argues, where jurisdiction is compulsory and non-state actors can initiate litigation); administrative review (to determine the consistency of international and domestic administrators’ actions with international law); and constitutional review (to do the same for international and domestic legislation).

Having mapped the population of international courts and explored their historical origins, Alter devotes the bulk of the book to “politics,” theorizing and examining empirically how courts promote changes in state behavior “in the direction the law indicates” (p. xvii). In Chapter 2, she begins by laying out three ideal-type models of IC influence, which she labels the “interstate arbiter,” “multilateral adjudication,” and “transnational politics” models. Alter then presents her own, “altering politics” model as a synthesis of the previous three models, although in practice it comes closest to the transnational politics model, indebted to and building upon the work of liberal scholars like Anne-Marie Slaughter, Laurence Helfer, Alec Stone Sweet, Miles Kahler, Andrew Moravcsik, Beth Simmons, and Christina Davis. Like those scholars, Alter emphasizes the role of domestic “compliance constituencies,” who both litigate cases and subsequently bring pressure on governments to comply with IC rulings. In this view, the influence of ICs depends crucially on the presence or absence of powerful, mobilized domestic compliance constituencies.

The third and final part of Alter’s story, “rights,” does not refer narrowly to international human rights courts (although, these feature prominently in the book), but more broadly to the claim that “delegation to ICs helps generate rights by allowing rights holders or defenders to ask judges for a legal remedy” (p. 5). As such, rights and remedies do not form a separate section of the book, but are woven into the other chapters. Alter shows how ICs validate and even create legal rights as well as remedies for their violation. The existence of these remedies in turn mobilizes litigants to claim those rights in a dynamic, virtuous circle.

Alter presents her book as an exercise in theory generation rather than testing, and her method as inductive and qualitative (p. 24). She therefore devotes the majority of the book (Chapters 4–8) to a wide-ranging set of 18 case studies of international litigation, designed to explore the causal pathways whereby ICs are activated by litigants and in turn activate domestic pressures for compliance. Alter presents her case studies as “hard cases” for ICs, which in every case rule against the strongly expressed preferences of respondent states. In several of Alter’s cases, states fail to comply or do so only in part, but across a wide range of cases, she finds similar patterns whereby new-style courts mobilize compliance constituencies and induce behaviorial change even among powerful, and/or illiberal, states.

Despite its broad scope, Alter’s book deliberately sets aside several important issues and questions, of which I mention just two. First, although Alter frequently refers to the international judiciary, The New Terrain of International Law generally treats ICs as unitary actors, seldom analyzing or mentioning the backgrounds, preferences, incentives, votes, or decisions of individual judges, or the disagreements among them. In this sense, Alter’s book can profitably be read alongside Daniel Terris, Cesare Romano and Leigh Swigart’s The International Judge: An Introduction to the Men and Women Who Decide the World’s Cases (2007), which opens the black box of courts and explores the preferences, incentives, and legal philosophies of judges in detail.

Second, and on a related note, Alter shows little interest in grappling with the question of judicial independence, which has been a prominent, perhaps even the predominant, theme in previous international relations scholarship on ICs. Alter is careful to note that she does not assume that her trustee courts are entirely independent, and that indeed ICs depend on domestic compliance constituencies for influence. Yet the notion that international judges might be influenced by career incentives or political pressures is dismissed early in the book (pp. 42–3), and is absent from the case studies, which essentially take IC rulings as given and explore their domestic and international effects. Alter presents this neglect of the question of judicial independence, and the redirection of attention toward the reception of judicial decisions, as a virtue—an escape from an unfalsifiable set of claims about member-state control of ICs. “The real issue,” she writes, “is that we can never really know why governments or judges make the decisions they do” (p. 338). Rather than engage in a fruitless effort to assess judges’ real motives, or states’ influence on them, Alter engages in an effort to understand how ICs move states in “the direction indicated by the law” (p. 358).

The weakness in this approach, however, is that it ignores a core insight of legal realism: International rules are frequently vague and admit of more than one plausible reading. As a result, “the direction the law indicates” is often indeterminate. Indeed, it is precisely because international law is subject to multiple, plausible interpretations that states delegate to ICs the authority to say what the law is. Yet the same indeterminacy that makes ICs valuable to states also grants international judges considerable discretion in their interpretation and application of the law. ICs can therefore be alternately audacious and activist or cautious and deferential, and they can be (at least among courts like the International Court of Justice and the European Court of Human Rights that allow for open judicial dissent) bitterly divided in their rulings. Taken together, these twin pillars of legal realism—the indeterminacy of law and the de facto discretion of judges when interpreting that law—mean that the effort to understand why international courts rule the way they do, including the questions of judicial independence and state influence, remains an indispensable part of any broader effort to understand the role of ICs in the international system.

Finally, while the tone of Alter’s book is understandably celebratory about the revolutionary power of ICs to promote the rule of international law, a cautionary note may be in order. It is striking that, while a remarkable 18 ICs were indeed created in just 12 years between 1992 and 2006, no new courts have been created since then, and one, the Southern African Development Community Court, has been suspended by its members and its jurisdiction curtailed by removing the right of individual initiative (p. 58). As Alter notes, it is too early to tell how the many young ICs will develop in the coming years, but it may be that Alter’s new-style ICs, which are robust in Europe and increasingly in Latin America, remain fragile in Africa and elsewhere—hothouse flowers in a world not yet fully purged of either domestic authoritarianism or international realpolitik. This possibility, however, only increases the value of Alter’s book, an indispensable guide to the workings, the promise, and the limits of international courts in world politics.