Barbara Koremenos’s The Continent of International Law: Explaining Agreement Design is in some ways the acme of the rational institutionalist approach to international relations; therefore, it showcases both the remarkable achievements of that framework and the diminishing returns it now faces.

Koremenos’s argument is straightforward: States design institutions rationally and purposefully “to overcome the harsh political realities” of international relations (p. 2). In this view, specific features of international institutions—e.g. withdrawal clauses, dispute settlement mechanisms, voting rules, etc.—are products of the underlying cooperation problem states face, such as the level of uncertainty or the severity of the distribution problem, and the aggregate characteristics of the states in question, such as their power relative to each other. To demonstrate this claim, Koremenos has carefully assembled a vast empirical cache that records some 500 data points for each of a sample of 234 international agreements. From human rights, to trade, to security, these institutions follow a common rationalist logic, Koremenos argues, showing how the agreements in her data conform to 12 “conjectures” that posit probabilistic relationships between different cooperation problems and specific institutional arrangements. For example, sharper distribution problems lead to more escape clauses, while more asymmetrical power relations lead to slanted voting rules. For Koremenos, these regular patterns, based in the rational behaviour of states, mean that international order forms a unified “continent of international law”—or COIL, as the book puts it—which plays a central role in world politics.

In COIL Koremenos brings together her and her co-authors’ previous work on Rational Design (RD) and forges new ground, expanding the RD framework to include new cooperation problems and conjectures, and cementing these theoretical arguments on a vast empirical foundation. The result is a magnum opus of RD. As such, it powerfully reaffirms the basic rationalist premise at the heart of so much contemporary IPE scholarship. But, somewhat paradoxically, the success of that paradigm has pushed the cutting edge of IPE research beyond the shores of Koremenos’s continent, into the archipelagos of mid-level theory, the deep sea trenches of historical institutionalism, the subterranean caverns of domestic politics, the clouds of transnationalism, the atmospheric currents of behavioural science, or other realms that depart from the rationalist, state-centric, unitary actor, ahistorical assumptions that undergird COIL. The central question for the reader is thus whether COIL is sufficiently compelling to refocus our attention on the continent Koremenos sees at the center of the intellectual map of IPE, or if the exercise simply reminds us of its existence.

Koremenos’s map of the continent reflects her previous experience as a cartographer. COIL deploys an elaborate theoretical apparatus that subsumes much of the RD work, trading “parsimony for accuracy” (p. 10). A strength of the book is, appropriately, to rationalize what could have been a sprawling laundry list of explanatory and dependent variables into organizing concepts like “centralization” or “control” that allow Koremenos to buy quite a lot of accuracy for relatively little loss of parsimony.

One may have wished, however, for slightly less parsimony in COIL’s elaboration of its theoretical claims. COIL seems to assume that the reader will accept much of this logic without objection, describing its 12 conjectures (and the more specific operationalizations of them that appear in the empirical chapters) surprisingly tersely. In other words, COIL presents its theoretical claims, but does not invest many pages in arguing for them by defending the plausibility of their assumptions or detailing their micro-foundations. Most strikingly, COIL includes a robust defense of game theoretic approaches to IR theory (pp. 57–59), but does not include any actual game theory to demonstrate the logic it deploys. As a result, the book’s theoretical contribution is to increase the depth and precision of the RD approach, but not to defend its basic assumptions or explore anomalies or exceptions that might enrich—or perhaps undo—it.

This confidence no doubt stems in large part from the book’s extensive and impressive empirical contribution, which unfolds across seven detailed chapters. As Koremenos notes, a particular strength of the COIL dataset is that it considers four different issue areas (economics, environment, human rights, and security), and creates a dataset that draws a meaningful sample within each area from the United Nations Treaty Series (Appendix 3 provides a helpful discussion of selection issues in related datasets and how COIL is able to mitigate them). IR scholars will no doubt make significant use of this public good (the COIL data are available for download), which could be used as an alternative to the widely used Correlates of War IO membership data.

While it is beyond the scope of this brief review to discuss COIL’s empirical findings in detail, the central result is robust evidence in favor of the 12 conjectures. Not every conjecture is supported by the data, but the statistical analysis broadly confirms that the patterns hypothesized describe the continent in the way Koremenos argues. This result is a powerful demonstration of logical coherence in international law, and is the book’s greatest contribution.

That said, the empirical approach also raises some questions about how to interpret the results. Most of the analysis consists of probit, logit, or OLS regressions that find correlations between the variables identified in the conjectures. As Koremenos notes, this puts the work more in the realm of comparative statics than causal identification, which is appropriate given the nature of the conjectures. That being said, in several cases the regressions consider additional complications, such as by taking conjectures in combination, as opposed to individually. Koremenos presents theoretically plausible reasons for these departures from the book’s basic theoretical apparatus; however, without more theoretical elaboration such moves could also been seen as ad hoc. Similarly, various control variables are sprinkled into the analysis, like regime type or whether or not an agreement includes the United States. COIL briefly connects these factors to their theoretical bases (e.g. theories of domestic politics, hegemony), but none are developed as meaningful alternative explanations, and so they again take on an ad hoc quality. Finally, COIL makes effective use of anecdotal information regarding certain international agreements to exemplify the logic of the conjectures. While they are readable and engaging examples of the dynamics COIL describes, these qualitative snippets are not able to provide additional evidence for COIL’s theoretical arguments because the observable implications of the hypotheses for qualitative data are never laid out. Again, more attention to the micro-foundations of the theories would have been helpful in this regard.

The core idea that Koremenos pulls from this vast project is that international law matters because states create it rationally. To understand this contribution, it is important to situate it in a relatively long arc of intellectual history. IR scholars began to use rational choice to explain systematically the emergence and function of international institutions in the 1980s. Institutionalism originally intended to modify realist theories, which could only account for institutions as extensions and epiphenoms of state power. By the early 1990s, however, institutionalism and realism had come to be treated (explicitly or implicitly) by many scholars as alternative “-isms” battling for dominance. As is often the case when paradigms come to see themselves not as competing explanations but as intellectual enemies, scholars sometimes framed their research around questions that were more useful as swords for disciplinary civil war than as ploughshares to cultivate our knowledge of world politics. One such distraction was the question of whether international institutions “matter” or not. The productive version of this question (how, and under what conditions, do international institutions affect state behaviour and other outcomes of interest?) was too often reduced to a binary and ultimately trivial debate. Happily, out of these paradigm wars emerged a rationalist approach to IR that took anarchy, power, and institutions seriously. In IPE, at least, rational institutionalism became the dominant approach within the discipline, and remains so today.

In some ways, COIL does not seem fully aware of this status, directing its contribution to an older literature. Koremenos asserts that IR has not paid sufficient attention to international law (p. 6), but then cites a range of studies that do exactly that, including her own work over a distinguished career. The book emphasizes the contribution of the dataset by stating, “Until recently, the empirical side of the field of international cooperation consisted mostly of case studies,” which would surprise the generations of scholars, many of whom are cited in COIL, who have made their careers around the quantitative study of preferential trade agreements, bilateral investment treaties, human rights agreements, environmental treaties, or similar work. The reader therefore wishes that Koremenos would have extended her discussion of how her ‘continent’ and the rationalist ideas that define it relate to other features of the contemporary IPE landscape. COIL succeeds in affirming the importance of rationalist theories of institutional design. But, focused on deepening a well-established paradigm, it is able to tell us much less about how and why such ideas matter. How much more is there to discover on this continent?