Is the international order a constitutional one? This question lies at the heart of this important new book. Karolina Milewicz argues that the world order is indeed becoming more constitutional through the creation of international treaties. This constitutionalization of the international legal order results from what Milewicz calls the “logic of democratic power” (p. 2). The book comes in two parts. The first sets out constitutional theory, combining theories from domestic constitutional theory with the distinctive characteristics of global politics. This reading of constitutional theory into global politics is not a simple application of one realm to another; rather, it demonstrates how a creative reading of theory at the international level can help us see international law and institutions in a new light. The second part makes the case that democratic states create international treaties which then “trap” them and the wider international community into a more constitutional world order. The unintended consequences of drafting, ratifying, and complying with treaty obligations has resulted in an international order in which the rule of law and international institutions have become much stronger. Milewicz tests her hypothesis on a dataset of 75 international treaties that have global reach, along with a more focused discussion of the International Covenant on Civil and Political Rights (ICCPR). Her results provide robust support for her hypothesis, providing important empirical evidence for scholars of international law and institutions.

This is a very good book. As Milewicz notes, much of the existing literature on international and global constitutionalism is either descriptive or theoretical. One of her most important contributions is to bring new empirical data to bear on the question of constitutionalism at the international level. The book also makes an important intervention into international relations (IR) theory. She notes that scholars often fail to combine the idealism that characterizes so much of the literature on international law and organizations with a realist attention to power. So, for instance, she argues that powerful democratic states play a key role in constitutionalizing the world order. Dividing the world into four categories of states—powerful and weak democracies and powerful and weak authoritarian states—might miss some of the nuances of the international order, but it nicely combines the realist focus on power with the liberal institutional concern with regime type. Because of this, the book speaks to those on both sides of this important IR theory divide.

Outside of the important theoretical and empirical contributions this book makes to global politics, it could benefit from a more inclusive approach to disciplinary and methodological standards. To study either global or international constitutionalism, scholars must take an interdisciplinary approach; the very nature of constitutionalism requires attention to both law and politics (and even culture and ethics). In fact, this book would benefit from a slightly wider understanding of work going on within political science rather than turning to other academic disciplines. First, in making the case for a more “empirical” approach to the topic, Milewicz relies on a particular understanding of social science, one that privileges quantitative and statistical analysis. In addition, Milewicz seems to assume that IR theories are limited to realism and liberalism. Together, these two ways of understanding her task prevent her from drawing on the rich qualitative material that constructivist authors of international relations have provided in recent years. For instance, Antje Wiener’s 2018 book (Contestation and Constitution of Norms in Global International Relations) uses qualitative evidence (cases and interviews) to reveal the various norms surrounding global constitutionalism, including the strength of those norms and their contested nature. There is little mention of this work on norms—an important body of research that supports some of the arguments made by Milewicz yet also posits some important challenges to her framing of the question. Although norms cannot be as easily quantified as numbers of states involved in crafting treaties or numbers of reports on compliance, understanding how they function at multiple global levels is crucial to understanding how constitutional the global order really is.

A second boundary that Milewicz imposes on her study comes from her definition of constitutionalism. The first part of the book is an excellent introduction to the theories and history of constitutionalism. Its focus on the American, British, and Swedish constitutions is especially helpful when she translates those largely domestic ideas into international ones. But in defining constitutionalism largely through the rule of law, the separation of powers, and rights, she leaves out one of the most important but also empirically slippery concepts in constitutional theory: constituent power. Constituent power is the idea that a constituent rests on a people—not only at its foundation but at key points throughout the life of a constitution. This differs from democracy in that constituent power is not a form of governance but a foundational justification for the existence of a constitution. The literature on this topic comes out of critical theory, drawing on German thinkers such as Jürgen Habermas. Although Milewicz shows an acquaintance with Anglo-American theories of constitutionalism and a very good grasp of histories of constitutional practice, some of this more European continental work would point her to this important theoretical framing within constitutional theory.

This concern is not only a definitional one, because it leads to one of the most important gaps in the book. The book argues that powerful democratic states create and comply with international treaties to create a more constitutional international order. The most powerful democratic state in the current international order is the United States. Yet, as any student of international law knows, the US has long stayed outside many key international treaties and institutions. Milewicz notes this—although it is buried in a discussion of her empirical data—and dismisses it as a result of American exceptionalism (p. 216). One could explain this resistance as a product of a particular reading of American constituent power rather than a peculiarity of American political culture. A similar reading could be made of the Brexit debate in the United Kingdom. This is not to say that such unilateral policies are justified. Instead, it is to say that they should not be dismissed as quirks. They reflect a fundamental challenge to a global constitutional order, a challenge that derives from an important constitutional principle.

Throughout the book, Milewicz appears to avoid the phrase “global constitutionalism” often, preferring to focus on international constitutionalism. The distinction is important because a global constitution is closer to a cosmopolitan order than to a state-based system advanced through traditional treaty making. Some, such as Chris Thornhill, have argued that human rights and judicial practices at national, regional, and global levels are helping to create something like a global constituent power that may well lead to a more robust global constitution. This literature is growing, and it could have been explored to support some of the claims Milewicz makes. Indeed, these judicial practices similarly are not intending to create a global constitution but may well be contributing to the creation of one.

Despite these disciplinary boundaries, Constitutionalizing World Politics is an excellent book. It provides one explanation for how inadvertent constitutionalization can happen. Combined with some of the constructivist and critical theories mentioned here, Milewicz’s book gives us new insights into how a more constitutional—hence cooperative—global order may well be emerging.