The comparative study of aspects of foreign relations law has a long tradition, primarily a transatlantic one.Footnote ¹ However, Curtis A. Bradley, co-editor-in-chief of this Journal and editor of the stupendous volume under review, the Oxford Handbook of Comparative Foreign Relations Law, assesses the state of research quite accurately, when claiming that this book seeks to lay the groundwork for “comparative foreign relations law” as a new field of study and teaching (preface, p. vii). Compared to previous efforts, the ambition of the Handbook is to establish comparative foreign relations law as a “field.” For this purpose, Bradley defines foreign relations law as “the domestic law of each nation that governs how that nation interacts with the rest of the world” (Bradley, p. 3). This definition is obviously familiar to lawyers in the United States. Yet, as Campbell McLachlan quite rightly clarifies in his chapter, “foreign relations law” is neither a legal term of art nor is it a category of the law with wide acceptance across national legal systems (McLachlan, p. 21). For example, the concept is extraneous to Spanish law. Nonetheless, most chapters in the volume share the constructive view that the domestic law governing international interactions may well be described—or at least meaningfully reinvented—as foreign relations law (for Spain, see the chapter by Espósito, pp. 205, 220).

While the whole project is driven by optimism that foreign relations law is a productive new field of study, only some contributors explicitly address the question of whether a certain domestic law they examine comprises a “foreign relations law.” Others remain silent on this point. By all means, it is one of the virtues of this volume that the editor and contributors reflect the “arbitrariness” (Bradley, p. 18) and the policy dimension behind defining foreign relations law as a “field.” Moreover, the editor was wise enough to allow for “reasonable disagreements about how best to define the field of study, and about what tools we should use to analyze it” (preface, p. ix). The volume was prepared with the utmost effort and with exemplary care. It is the outcome of a series of conferences held in Geneva, Tokyo, Pretoria, and Leiden between 2015 and 2018. In the course of preparing the volume, the editor also assembled a number of related shorter essays in an AJIL Unbound symposium.Footnote ²

The general approach of the book is functional. Contributions compare how the functions of foreign relations law are fulfilled in different jurisdictions, and what the major premises of a given foreign relations law are. The editor ensured a certain pluralism of methods. While Part I is mostly conceptual, the rest of the book is mainly descriptive. Most parts are introduced by a general conceptual or empirical chapter aiming at a more or less global survey. A number of chapters in Part I and of the introductory chapters to other parts, written by Tom Ginsburg, Oona A. Hathaway, Jenny S. Martinez, Pierre-Hugues Verdier and Mila Versteeg, and Laurence R. Helfer, are based on the Comparative Constitutions Project, a data set coding the world's constitutions since 1789.Footnote ³ Accordingly, these chapters are mostly quantitative in their comparative analysis. Other introductory chapters raise more conceptual issues like the chapter by Duncan B. Hollis and Carlos M. Vázquez on the endogenous or exogenous origins of foreign relations law. The part on federalism directly jumps into national reports. While some chapters include comparative aspects only in their conclusions (Kadelbach, p. 189), others are truly comparative. Only one chapter, by Joris Larik, chose the EU and the Association of Southeast Asian Nations (ASEAN) for a symmetric comparison.

Bradley assembled an impressive list of distinguished scholars and practitioners from all over the world who are experts in their fields. The volume comprises seven parts. Part I considers general issues about how to define and study comparative foreign relations law as a field. Bradley begins the part by describing the field of foreign relations law and providing a summary of its history in the United States. Thereafter, Campbell McLachlan sets out five conceptions of the function of foreign relations law. While “the set of problems that foreign relations law investigates are ones that all states must resolve” (Bradley, p. 21), McLachlan explains that the major premises underlying the field vary. According to his taxonomy, the functions of foreign relations law can be more exclusionary or more internationalist, emphasize concerns of constitutional law, or focus on diplomatic functions or on allocating spheres of jurisdiction and defining the applicable law. Given that comparison is necessarily generative, Karen Knop regards the field of comparative foreign relations law as an “invention” and as an “analytical frame” and carefully exposes the “trade-offs” of introducing this field. In a similarly thoughtful approach, Oona A. Hathaway analyzes the opportunities and challenges of a comparative foreign relations law agenda and its broader implications. She notes the difficult methodological issue that rules of foreign relations law are embedded in and intertwined with a given state's unique legal, historical, and political context. Between these two chapters, Tom Ginsburg highlights that structuring international relations is one of the central functions of national constitutions (Ginsburg, p. 63) and explores the potential complementarity between international and domestic law in an optimal constitutional design. In the remainder of Part I, Jenny S. Martinez and Alejandro Rodiles address the relationship of executive and legislative powers over foreign relations. While Martinez offers a general theoretical account and a descriptive analysis based on the Comparative Constitutions Project, Rodiles makes the normative case for “inventing” a Mexican foreign relations law. According to Rodiles, using the foreign relations law lens draws attention to some outstanding legal problems so far not addressed by lawyers in Mexico, for example how to deal with trends toward informal international lawmaking beyond formal treaties or other traditional sources of international law.

Part II addresses the domestic processes that nations use for concluding international agreements. Based on a quantitative global survey, conducted with data from the Comparative Constitutions Project, Pierre-Hugues Verdier and Mila Versteeg outline four trends relating to treaty-making and withdrawal: a greater parliamentary participation in approving treaty ratification; the emergence of “workarounds” which allow the executive to bypass parliamentary approval for certain agreements, but usually result in those agreements having lesser domestic legal status; an emerging trend toward parliamentary approval of treaty withdrawal, usually for those treaties whose ratification required such approval; and a more active role of the judiciary in policing treaties through both ex ante and ex post constitutional review. All four trends move away from the executive-dominated world of traditional treaty relations (Verdier and Versteeg, p. 155). Jean Galbraith, Stefan Kadelbach, Tadaatsu Mori, Carlos Espósito, and Jaemin Lee contribute studies of the relevant law and practice in the United States, Germany, Japan, Spain, and South Korea, respectively; Marise Cremona examines EU foreign relations law concerning the making of treaties and other international agreements. An important insight across jurisdictions is that the notion of the treaty under international and under constitutional law is to be distinguished, and this distinction allows for variations in domestic procedures. Chapters in other parts of the Handbook add further insights on the relevant law of treaty-making and this distinction (see Côté, pp. 285–86, on Canada).

Along the way, the tour undertaken in Part II also illustrates the various sources of foreign relations law: while foreign relations law is recognized as a field of law in the United States and Germany, Galbraith underscores that in the United States, it owes more to precedents and practice than to the text of the U.S. Constitution (Galbraith, p. 171). For Germany, Kadelbach focuses on the constitutional change brought about by the German Federal Constitutional Court. In Japan, a statement of a former foreign minister, the so-called Ohira Principles of 1974, continues to serve as guidance (Mori, p. 191). In Spain and South Korea, by contrast, treaty-making is subject to explicit legislation. Since 2014, Spain has adopted new ambitious and detailed pieces of foreign relations legislation, including the 2014 Treaties and Other International Agreements Act, the 2014 law of external action policy and service, and the 2015 law of foreign state immunities (Espósito, p. 207 et passim). South Korea also adopted new legislation, the Act on Governing Procedures of Conclusion and Implementation of Trade Agreements of 2011 (Lee, pp. 234 et seq.). This shows that the field of foreign relations law can be dynamic without being recognized as such.

Part III focuses on how federalism impacts the conduct of foreign affairs. While the interest in this focus is certainly driven by the U.S. experience (see the chapter by Ernest Young), federalism is also relevant for foreign relations law in other places. Chapters by Charles-Emmanuel Côté, Roland Portmann, Anamika Asthan and Happymon Jacob, and Robert Schütze, respectively, demonstrate this for Canada, Switzerland, India, and the European Union. Interestingly, the Federal Republic of Germany is missing in this part; it is at least debatable whether it is possible to study the federal relations law of Germany without dealing with federalism (for the claim that this is impossible with respect to Canada, see Côté, p. 277). Actually, while the role of the German Länder in foreign relations is comparatively limited, debates on their role in the implementation of international treaties are similar to the debates in other federal states. Even so, the insights gained from reading Part III extend beyond federal states. The chapters in this part highlight the complexity of constitutional structures, which resist simple categorizations, and the limited effects of constitutional texts as compared to actual practice. If anything, this part teaches us that a pervasive overlap between foreign and domestic concerns, a continuing domestication of international law, and disaggregation of the state (Young, pp. 273–74) compromise the capability of foreign relations law to perform its functions.

Part IV explores how nations engage with, and disengage from, international institutions. This part, with chapters contributed by Laurence R. Helfer, Paul B. Stephan, Paul Craig, Andreas L. Paulus and Jan-Henrik Hinselmann, Hannah Woolaver, and Joris Larik, is relatively diverse, addressing both participation in treaties and membership in international organizations. It is remarkable and indicative of the state of affairs that disengaging from international institutions—a topic that did not attract much attention for decades—has now become a major concern due to the current general backlash against globalization and due to “Brexit” in particular (Paulus and Hinselmann, p. 420). The geographical focus in this part is on the United States, the United Kingdom, Germany, and South Africa. Given international law's general indifference toward domestic law, the interplay of the international law of treaties and the complex domestic law and procedures that safeguard democratic participation and deliberation carries a potential for “mismatches” (Helfer, p. 370) in all these states.

Contributions to Part V compare how nations apply international law within their domestic legal systems. Hollis and Vázquez examine self-execution of treaties in the United States and around the globe, with an interest in identifying and explaining exogenous and endogenous origins of foreign relations law. Shaheed Fatima, Gib van Ert, Amichai Cohen, Hiromichi Matsuda, and Congyan Cai, respectively, analyze the practice of British, Canadian, Israeli, Japanese, and Chinese courts. Regional studies by René Urueña and Ernest Yaw Ako and Richard Frimpong Oppong investigate Latin America and Commonwealth African countries. Finally, Mario Mendez examines the application of international law by the Court of Justice of the European Union. These chapters offer valuable insights and demonstrate that there is a lot to learn about foreign relations law. Cohen, in his contribution on Israel, makes a point of more general interest for the study of foreign relations law: when reviewing security measures in the territories, the Israeli Supreme Court did not apply international law in the traditional sense. Rather, the Court enriched international law with concepts of individual responsibility and proportionality adopted from its own domestic human rights jurisprudence and, on that basis, balanced human rights and security considerations (p. 526). This clearly demonstrates the “hybrid” nature of foreign relations law.Footnote ⁴

In Part VI, David P. Stewart, Philippa Webb, Hennie Strydom, Andrea Bianchi, William S. Dodge, and Eirik Bjorge and Cameron Miles consider how nations apply rules of sovereign and foreign official immunity and also more generally how they take account of norms of international comity. The concluding Part VII examines how nations structure decisions to use military force. Monica Hakimi's general chapter on techniques for regulating military force is followed by national reports by Bradley on the United States, Katja S. Ziegler on the United Kingdom, Anne Peters on Germany, Mathias Forteau on France, and Tadashi Mori on Japan.

The reading of these texts provides many valuable insights in dynamic and vital areas of the law. The Handbook is an unparalleled and reliable source of knowledge for the foreign relations law in many states. Moreover, it makes accessible further literature, mostly in English. It is not only an impressive scholarly achievement in itself, but serves as a rich hub for future research, in the true spirit of a research handbook. As Bradley writes, there is much that we still do not know about foreign relations laws and practices around the world (preface, p. ix). The Handbook will hopefully lead to much more comparative work on foreign relations law.

That said, the volume also reveals a number of problems to be tackled going forward. As McLachlan notes, it is remarkable that the relationship between public international law—the legal system that all states have in common—and national legal systems in the exercise of foreign relations has to date proved so resistant to comparative investigation (McLachlan, p. 43). Foreign relations law, for the very fact that it ties in with international law, seems to be a natural candidate for comparison. And yet, foreign relations law is “double-facing.”Footnote ⁵ It looks outward to the relations of the state with other states and looks inward to define the impact of the international upon the domestic sphere. This makes comparison difficult. Traditional distinctions of common law and civil law, dualism and monism, presidential and parliamentary systems, and federal and unitary states have already proven to be of little avail. The same applies to general categorization of state institutions as democratic or nondemocratic, liberal or nonliberal, or presidential or parliamentary (cf. Kadelbach, p. 189, and Hathaway, pp. 87–88). While the field is still in need of more fined-grained analysis, more conceptual work is also needed in order to define a vocabulary and a framework of analysis. Apart from this, some chapters of the volume demonstrate the significance of culture. For example, Espósito notes that a culture of democratic scrutiny of treaties is simply absent from Spanish parliamentary practice (Espósito, p. 217). Comparative studies cannot ignore such cultural factors, and this makes comparison more demanding, too.

To be sure, there are many common themes. One of them is how constitutional ideas “migrate”Footnote ⁶ in the area of foreign relations law and how developments on the international plane and local needs trigger the development of the law (Ginsburg, p. 70; Kadelbach, p. 189; Lee, p. 222). Moreover, many countries, especially constitutional democracies, are struggling with similar foreign relations law questions, including: How can legislatures stay involved in foreign affairs decision making despite having less access to information and less ability to act quickly than the executive? How can nations preserve domestic constitutional values and structures in the face of globalization and transnational governance? Should courts police allocations of foreign affairs authority or instead leave it to political actors to work this out among themselves? How can courts and other actors reconcile tensions between maintaining good relations with other nations and giving effect to fundamental norms of international law? (preface, pp. viii). Arguably, a common trend can also be identified—or at least debated—for several jurisdictions: an established foreign affairs “exceptionalism” in the United States and other states (with regard to justiciability or executive power) is giving way to a process of “normalization”Footnote ⁷ (see Bradley, pp. 13–18, on “foreign affairs exceptionalism;” Portman, pp. 302–04, on Switzerland).

At the same time, this analysis is informed by the language and structure of U.S. foreign relations law—which certainly provides one of the “best-stocked cabinet[s] of issues and ideas” (cf. Knop, p. 46). Of course, it is useful to make every effort to include underrepresented states (cf. Hathaway, p. 84). The comparative project of the Handbook has already moved away from the U.S. paradigm, with its focus on case law and the work of the judiciary. Applying this perspective to different contexts can be fruitful, as Rodiles demonstrates. Yet, in contrast to Rodiles, Urueña argues that the foreign affairs legal field builds on a premise—a strictly national vantage point for public law, from where to look at the international—that is not applicable to Latin American constitutions (Urueña, p. 581). This points to a more fundamental issue. Comparative foreign relations law carries the risk of transplanting legal concepts and epistemic categories that developed in a specific frame of reference into different contexts. Both the meaning and the social function of legal concepts like the distinction between international and domestic law, separation of powers, self-determination, and individual rights will vary with context. Therefore, we cannot simply take similarity as a starting point. Rather, we must take seriously different historical and political-economic contexts shaped by different varieties of constitutionalism, geopolitical positions, and epistemic frameworks.Footnote ⁸ Notably, for many postcolonial states, foreign relations did not begin as interstate relations but as dealings between chartered trading companies like the East India Company and local rulers.Footnote ⁹ The experience of statehood was also different: the international preceded the national; and statehood was produced and defined by international law during decolonization. For many new states, decolonization meant political independence but continued economic dependence: they depended on imports of capital and technology and on volatile exports of primary commodities, which were often foreign-owned or locked into unequal concessions agreements. This context gave rise to legal thinking about foreign relations with different conceptions of sovereignty, collective self-determination, and rights. It is based on transnational and hybrid categories that transcend the binary opposition between national and international, it includes legal subjects ranging from state and individual to corporations, indigenous peoples, and rights of nature, and it is geared toward enhancing economic self-determination, socioeconomic development, and equality. In short, this “peripheral” foreign relations law is broader than the “liberal” one: it includes economic relations with powerful nonstate actors and aspects of economic constitutionalism.Footnote ¹⁰

The Handbook also raises the issue of the relationship of foreign relations law and international law as fields of study. Adding a comparative perspective might help to moderate any (real or perceived) insularity (Galbraith, p. 157) or “parochialism.”Footnote ¹¹ As Knop writes in her contribution, U.S. foreign relations law may be the reason why U.S. international lawyers need comparative international law (Knop, p. 50). Comparative work may promote engagement among states in the exploration of a common issue of great importance: the regulation of the interface between international law and national constitutions in the control of the external exercise of public power (McLachlan, p. 43). However, introducing comparative foreign relations law and transferring the foreign relations law perspective to other states may imply a turn away from international law. There is a risk of displacing, discounting, and distorting international law (Knop, pp. 51–57). A dominant foreign relations law perspective might facilitate the creation of parochial national views of international law. To be sure, an international law that is truly international is rather a regulative ideal than actually viable.

Indeed, as Bradley writes, the comparative study of international law pursued by Anthea Roberts and othersFootnote ¹² involves a different project (Bradley, p. 5). The difference lies in the subject of investigation, which overlaps only partially. Foreign relations issues can operate below international law's radar, as the trend toward informalization on the international plane and the involvement of substate actors demonstrates. U.S. and Commonwealth scholars also consider private international law to be a potential part of foreign relations law (Knop, p. 48). More deeply, comparative foreign relations law and comparative international law also differ in perspective. Comparative international law exposes the situatedness of international lawyers in their own national contexts and the politics of international law, and it unlocks the full critical potential of comparison or its “capacity for subversiveness” (id., p. 49). Comparative foreign relations law is more inward-looking and focused on constitutional values and separation of powers. It may be a coincidence that comparative foreign relations law is attracting increasing attention at a time when the international rule of law is widely viewed as in decline.Footnote ¹³

At any rate, the contributions to the Oxford Handbook of Comparative Foreign Relations Law demonstrate impressively that foreign relations law need not be parochial at all. While contributors assert that a supposed choice between national democracy and international legality is a false dichotomy (Paulus and Hinselmann, p. 413), comparative foreign relations law is key to understanding how to square this circle.