In The Closure of the International System, Lora Anne Viola grapples with the contradiction between two views among international relations (IR) scholars. On the one hand, the liberal approach to international institutions posits that the international system has become more inclusive, democratic, and egalitarian in the twentieth century with the globalization of international institutions and the spread of liberal democratic norms. On the other hand, an emerging literature in the field treats hierarchy as a key ordering principle of international politics. Rather than attempt to adjudicate between these views, The Closure of the International System proposes that equality and inequality represent two sides of the same coin.

To resolve the contradiction between hierarchy and sovereign equality, Viola turns to the Weberian concept of social closure. Weber defines social closure as the establishment of a boundary between a group and outsiders based on the group’s distinctiveness, which serves to justify the group’s exclusive access to valuable resources and opportunities (Max Weber, Economy and Society: An Outline of Interpretive Sociology, 1922). Viola astutely applies this concept to international relations, arguing that the formation of the modern international system narrowed the range of legitimate political actors. Whereas different types of actors enjoyed political authority during the system’s early stages, Viola notes, the sovereign state acquired unparalleled legitimacy over time. From a closure perspective, equality implies inequality: deciding which actors count as equals requires deciding which actors do not.

In chapters 1 and 2, Viola introduces her closure thesis and applies it to the formation of the modern international system. In particular, she combines the idea of social closure with “a materialist interpretation that understands institutions as providers of club goods” (p. 24). This argument involves two claims. First, international institutions provide goods to a limited set of actors, because only those political units recognized as independent enjoy legal personhood in international law and have access to system benefits like loans or disaster relief. Second, expanding the availability of such goods decreases the benefits for existing members, because membership heterogeneity increases transaction costs and creates demands for redistribution. Given this incentive structure, Viola claims, powerful members respond to pressures for inclusion by gradating rights within the club of sovereign states.

Based on this theoretical foundation, chapters 3–5 examine the formation of the international system since the fifteenth century. Viola aptly describes her approach here as “tak[ing] a bird’s eye view of politics in favor of teasing out a deeper structural logic” (p. 34). Each chapter focuses on a key institution that constitutes system membership: diplomacy, international law, and international organizations. Whereas IR scholars usually see each of these institutions as conducive to cooperation and democratization, Viola argues that they serve as mechanisms of closure that distinguish between those who count as equals (European territorial states) and those that do not (nonstate actors and non-European actors). Even as the system’s institutions expanded to include non-European polities in the twentieth century, Viola notes, recognition hinged on assimilation to European standards, and sovereign equality did not entail procedural equality or equal voice.

Chapter 3 highlights the diplomatic practices that constitute system membership. Whereas IR scholars typically see diplomacy as a tool of mediation following the dissolution of Christendom, Viola argues that diplomacy introduced selectivity to transboundary relations. Multiple types of principals and agents engaged in political communication after the fall of the Roman Empire, but the emergence of diplomatic practices narrowed down the range of legitimate participants in transboundary communication. Over time, those actors recognized as legitimate formed an exclusive, homogeneous group that enjoys privileged access to exclusive domestic jurisdiction, transboundary communication, and governance institutions. Diplomacy thus helped produce the system’s political boundaries, rather than merely serving to mediate among existing units.

In chapter 4, Viola argues that international law serves as a closure mechanism that delimits the range of political actors with legitimate access to the rights to self-rule, make treaties, and wage war. Examining the work of early jurists since the seventeenth century, Viola contends that powerful actors use international law to justify two forms of domination: exclusion, whereby only the territorial state is recognized as entitled to rights, and assimilation, whereby system membership depends on conformity to European standards. Because international law establishes equality among European territorial states by defining sovereignty in their image, it provides a basis for the inequality of other actors that are vulnerable to colonialism and intervention.

In chapter 5, Viola argues that powerful states control access to membership in international organizations (IOs) and its benefits. In response to pressures for membership expansion, core states adopt three strategies to protect their authority and interests: conditioning membership on assimilation into the European nation-state paradigm; allocating governance authority unequally among members, as in the creation of the UN Security Council; and creating new, exclusive organizations like the G20. To Viola, system expansion implied closure: as the number of IOs and states increased, the sovereign state became more narrowly defined based on the self-determination principle, to the detriment of alternative organizational forms. Moreover, newcomers’ demands for institutional recognition were met with new forms of exclusion.

The goal of her book, Viola explains, is to contribute to “a newly emerging literature concerned specifically with dynamics of stratification” (p. 11). In particular, Viola aims to make three contributions: (1) moving beyond an either–or view of hierarchy and equality in IR to theorize about the relationship between the two, (2) theorizing simultaneously about the social and material dynamics that underpin hierarchy, and (3) avoiding “the presentist bias in much of the IR literature … by taking a longer view of the development of the international system” (p. 22). The book accomplishes the first and third of these goals well. The chapters tease out the interdependence between sovereign equality and hierarchy, drawing our attention to political domination within institutions that IR scholars typically associate with equality. In addition, Viola’s wide-ranging applications cover formative moments in the development of the international system, highlighting alternative forms of political organization that were gradually winnowed out.

The book is somewhat less effective in accomplishing the goal of integrating social and material factors into the study of hierarchy. Viola’s choice to focus on the institutionalist and materialist dimensions of hierarchy (p. 11) has two implications. First, from a materialist perspective, matters of inclusion or exclusion become struggles over redistribution. This move leaves little room to examine those distinctive processes that characterize struggles for recognition. Second, from an institutionalist perspective, international outcomes derive from the intentionality of powerful actors. As Viola asserts, “Powerful members are in the structural position to determine the terms of inclusion and exclusion” in the club (p. 81). This move leaves little room to examine the processes of legitimation that sustain international order and neglects the structural constraints placed on all actors. As a result, Viola’s analysis privileges material or strategic factors over social or symbolic ones. But, overall, the book’s provocative argument and wide-ranging applications provide fertile ground for studies of hierarchy in international relations, like its author intended.