I Defining Foreign Relations Law

As defined in the Oxford Handbook, foreign relations law is ‘the domestic law of each nation that governs how that nation interacts with the rest of the world’.Footnote ² Such domestic law can take a variety of forms, including constitutional law, statutory law, administrative regulations, and judicial decisions. It can also include constitutional customs, or ‘conventions’, that may or may not have legal status.Footnote ³ Much of this law, at least in constitutional democracies,Footnote ⁴ concerns allocations of authority between political actors, such as the authority to represent the nation in diplomacy, to conclude and terminate international agreements, to recognize foreign governments and their territories, and to initiate or end the use of military force.Footnote ⁵ In federal systems, these allocation issues are not only horizontal but also vertical, extending to the relations between national and subnational institutions. Foreign relations law also encompasses issues relating to the role of the courts in transnational cases, such as whether certain issues are ‘nonjusticiable’ and thus subject entirely to political branch determination, whether and to what extent courts should give deference to the views of the executive branch, and the types of relief that courts are allowed to issue when they find that the executive branch has acted unlawfully.

Because foreign relations law under this definition is a type of domestic law, it is analytically distinct from a nation’s international legal obligations.Footnote ⁶ This distinction between foreign relations law and international law is not meant to suggest anything about the status of international law within a domestic legal system. Nations differ in the extent to which they are positioned towards either the ‘monistic’ or ‘dualistic’ ends of the spectrum with respect to the domestic status of international law, and these differences are themselves part of their foreign relations law.

One virtue of defining foreign relations law as a form of domestic law is that it facilitates comparative analysis. Unlike international law, foreign relations law makes no claim of universality and instead accepts that nations can and will have different approaches.Footnote ⁷ And there are many reasons why the content of foreign relations law might vary from nation to nation. It is not surprising, for example, to find differences between constitutional arrangements developed after World War II and those developed earlier. Parliamentary and presidential systems are also likely to reflect somewhat different approaches to questions of the separation of powers. In addition, understandings of the judicial role likely differ among countries, including as between civil law and common law countries. The particular domestic politics of a country can also have an important influence on the content of its domestic law, including its foreign relations law. Furthermore, foreign relations law may be affected by a nation’s geopolitical status and sense of its national interest, and these will obviously vary, both among individual countries and over time.Footnote ⁸

Another virtue of treating foreign relations law and international law as analytically distinct is that it allows for a consideration of the relationship between these bodies of law, including a consideration of the ‘bridges’ and ‘boundaries’ that are the focus of the present volume. As discussed below, there is an interactive dynamic between foreign relations law and international law, with each body of law having effects on the other.

Despite the benefits of using this definition for purposes of analysis, it should be emphasized that any sharp distinction between foreign relations law and international law will be artificial in practice. International law can and often is applied as domestic law, either directly or through some act of domestic incorporation. Moreover, even when international law is not applied directly, courts often construe domestic law in light of international legal obligations, and executive actors often exercise their discretion with such obligations in mind. Foreign relations law, as defined in the Oxford Handbook, includes the domestic rules governing such application and interpretation but not the international legal obligations themselves. The term could be defined more broadly, however, to include at least some aspects of international law.Footnote ⁹

Foreign relations law, however it is properly defined, has long been a more developed field of study and teaching in the United States than in most other countries. It is not entirely clear why this is so. The United States has the oldest written Constitution in the world, and accommodating that Constitution to a radically changed international environment, as well as a substantially different US role in that environment, may present unique challenges. In addition, the United States has a unique brand of federalism that tends to generate complex legal issues, especially as globalization has blurred the line between foreign and domestic affairs. Law schools in the United States also may have a more flexible structure than in many other countries, allowing faculty to more easily cross historic subject matter divides.

Whatever the reasons, there now appears to be growing interest outside the United States in foreign relations law. In 2014, Campbell McLachlan published an important and wide-ranging treatise on Commonwealth foreign relations law, a treatise cited by the UK Supreme Court in its landmark Miller decision concerning Brexit.Footnote ¹⁰ A number of important works have also been published in recent years focusing on EU foreign relations law, addressing issues such as the process for concluding international agreements and the role of federalism that are similar to the foreign relations law issues faced by individual nations.Footnote ¹¹ The Oxford Handbook, which has forty-six chapters by authors from around the world, will hopefully stimulate further international interest in the subject. Likewise, the present volume highlights the potential interest in foreign relations law by scholars from a wide variety of countries. As a result, this is an especially good time to be thinking both about the nature of this body of law and about similarities and differences in how nations address it.

II Foreign Relations Law’s Effects on International Law

There a variety of ways in which foreign relations law can affect international law. Most directly, a nation’s foreign relations law can affect the manner in which a nation engages with international law – for example, the domestic process that it must follow in order to join or implement a treaty. Sometimes such foreign relations law will, at least as a practical matter, act as a constraint on a nation’s ability to engage or comply with international law – for example, by requiring that multiple domestic institutions agree on such engagement or compliance. If so, this will have an impact on international law’s development.Footnote ¹² In some cases, domestic courts may even require that governmental actors take certain actions to ensure the compatibility of international law with domestic constitutional law. A noteworthy example is the Colombian Constitutional Court’s 2019 decision conditioning the constitutionality of a bilateral investment treaty between Colombia and France on the issuance of a particular interpretive declaration by the two countries.Footnote ¹³

Sometimes foreign relations law will affect not only international law’s primary rules, but also its secondary rules that govern how international law is made. Indeed, this has long been the case. For example, when some nations began separating the treaty power between executives and legislatures after the American and French revolutions of the late eighteenth century, international law began to relax expectations that signature of a treaty carried with it an obligation to ratify the treaty.Footnote ¹⁴ Similarly, in part spurred by American practice arising from its divided treaty power, international law came to allow for treaty reservations at the time of ratification (and international law on that subject has since evolved to take account of changes in the nature of treaty-making, including most notably the rise of multilateral conventions).Footnote ¹⁵ Today, the foreign relations laws of many countries divide the treaty power between the executive branch and the legislature, at least for certain types of agreements,Footnote ¹⁶ making these international law rules even more significant.

Importantly, the normative goals of foreign relations law will not always align with the normative goals of international law. For example, there is an effort in some countries to give their legislatures a stronger role in foreign relations decision-making, such as with respect to treaty-making and the use of military force. Doing so might lead to greater deliberation and democratic input, but it will not inevitably promote greater international cooperation. It is not uncommon, for example, for legislatures to fail to approve treaties or other international law efforts favored by the executive branch. There may also be a recent trend towards making foreign relations law more ‘administrative’ in nature, and thus potentially subject to greater judicial oversight. But, as Angelo Jr. Golia notes in his chapter for this volume, such a shift ‘does not always imply greater coordination among systems, but can rather bring more disorder, conflict and unpredictability’.Footnote ¹⁷

Sometimes a greater role for legislative or judicial involvement in foreign relations law will even lead to breaches of international law that might not have occurred under executive control. This is one way of understanding the much-discussed Medellin v. Texas litigation in the United States. In holding that legislative action was needed in order to convert the US obligation to comply with a decision of the International Court of Justice into domestic law,Footnote ¹⁸ the Supreme Court made it much more difficult for the United States to comply. Indeed, even now, many years after the decision, Congress has still not enacted the requisite legislation.Footnote ¹⁹ The US experience with amendments to its sovereign immunity statute in recent years similarly highlights how legislatures may not always prioritize international law compliance. The US Congress has created various exceptions to sovereign immunity for terrorism-related conduct, despite concerns raised by the executive branch that such exceptions may not be consistent with international law and might expose the United States to reductions in its own sovereign immunity abroad.Footnote ²⁰

Another widely discussed example is the 2014 Italian constitutional court decision issued in response to the ICJ’s decision in Germany v. Italy concerning the international law of sovereign immunity. In holding that the international law of immunity recognized by the ICJ was incompatible with Italian constitutional law and thus inapplicable in the domestic legal order, the court contributed to placing Italy in potential breach of its international obligations. In doing so, it acted contrary to the position of both the executive and legislative branches in Italy, which were prepared to accept the ICJ’s decision.Footnote ²¹ In these and other examples of potential conflict between foreign relations law and international law, there can be reasonable debates about which body of law should bear more of the blame. One interesting issue for future scholarly analysis would be whether and to what extent each of the two bodies of law has some responsibility to coordinate with the other.Footnote ²²

III International Law’s Effects on Foreign Relations Law

Not only does foreign relations law affect international law, but international law also in turn affects foreign relations law. As an initial matter, the foreign relations powers that must be allocated under foreign relations law are themselves often defined by international law, which regulates the rights and obligations of sovereign nations.Footnote ²³ For example, if a national constitution assigns the power to ‘declare war’ to a particular national actor, one would need to consult international law in order to have a full understanding of the potential scope and significance of this authority. More generally, as a matter of explication, it will often be necessary to know the international law backdrop in order to understand elements of foreign relations law, such as foreign relations law relating to treaty-making and interpretation, extraterritorial regulation, and sovereign immunity.Footnote ²⁴

Moreover, while international law generally purports to be agnostic about domestic constitutional arrangements, in fact it sometimes assumes or favors certain arrangements. In particular, international law tends to assume, at least as a default, executive control over aspects of foreign relations. As a result, international law can make it more difficult for nations to rein in executive authority in the foreign relations area. This is evident, as Edward Swaine notes in his chapter for this volume, in the international law governing treaty termination.Footnote ²⁵ The Vienna Convention on the Law of Treaties presumes that notices of treaty withdrawal received from heads of state are valid and, unlike for treaty formation, does not provide for any domestic process justification for voiding such notice. To be sure, international law does not require that states give unilateral withdrawal authority to their executives, and it is possible that domestic institutions could resist the exercise of such authority. In recent years, national courts in both the United Kingdom and South Africa famously insisted on legislative involvement in treaty withdrawals. But the effectiveness of such domestic checks will depend on a state’s particular laws and institutions.Footnote ²⁶ International law, as currently structured, does not itself facilitate legislative involvement in treaty withdrawals.

Executive authority is favored under international law in other ways as well. The Vienna Convention sets forth only very narrow grounds for invalidating treaties concluded in violation of domestic law: according to article 46 of the Convention, the violation must not only concern ‘a rule of [the nation’s] internal law of fundamental importance’, but the rule must also be ‘manifest’. In part because of this provision, the US Senate did not approve the Convention when President Nixon submitted it in the 1970s: the Senate Foreign Relations Committee was concerned that this provision might bind the United States to international agreements made by the president without the two-thirds Senate consent required by article II of the Constitution, because that requirement might not be considered ‘manifest’ given the extensive US practice of concluding agreements outside of this process.Footnote ²⁷ Again, of course, national institutions could resist executive aggrandizement in this area. In 2017, for example, the Ghanaian Supreme Court held that Ghana’s president had acted unconstitutionally in concluding an agreement with the United States without obtaining parliamentary approval, and it specifically declined to follow the US practice of allowing executive agreements.Footnote ²⁸ But, as for treaty withdrawal, any such domestic resistance will obtain little support from international law.

Yet another way that the Vienna Convention may empower executives is its treatment of signing obligations. Under article 18 of the Convention, a nation that signs an international agreement is ‘obliged to refrain from acts which would defeat the object and purpose’ of the treaty ‘until it shall have made its intention clear not to become a party to the treaty’. This is true even for nations that require legislative approval prior to the ratification of treaties. As a result, executives in such nations can potentially create treaty-related obligations through unilateral action. In the United States, this may have happened when the Clinton administration signed the Rome Statute for the International Criminal Court in 1999, knowing that the incoming Bush administration was not supportive of the Statute. The Bush administration then ‘unsigned’ the Convention by announcing that it had no intention of ratifying it.Footnote ²⁹

These examples also suggest that, especially in nations in which the scope of executive authority over foreign relations is unclear, executives may be able to leverage international law as a way around domestic constraints. Another potential example of this phenomenon concerns the use of military force. Even in nations that require legislative approval for some uses of force, executives may seek to rely on international law, such as UN Security Council authorization, as an alternative or supplementary source of authority. This happened in the United States, for example, in connection with the Korean War.Footnote ³⁰

Another example of international law’s potential effect on foreign relations law concerns the increasingly administrative nature of international law. A significant amount of international law is made today not through high-level negotiations between foreign ministries but rather through international institutions, lower-level negotiations between domestic administrative agencies, and various forms of ‘soft law’.Footnote ³¹ This development tends to further enhance executive authority over foreign relations, for a number of reasons: executive agents tend to represent nations in international institutions, administrative law tends to be centered in the executive branch, and less formal agreement-making may not be subject to the usual domestic requirements for treaty-making.Footnote ³² In response to this development, as Jean Galbraith notes in her chapter for this volume, legislatures may need to enhance process-based constraints on the exercise of executive authority.Footnote ³³

Sometimes international law itself requires or favors certain processes of decision-making, and when it does so this can also affect foreign relations law. In their introductory chapter for this volume, Helmut Aust and Thomas Kleinlein give the example of a requirement of environmental impact assessments,Footnote ³⁴ a requirement that may as a practical matter empower certain administrative agencies at the domestic level. Investment law is another example where international law may in effect mandate certain domestic processes, as well as the substance of some aspects of the domestic law applied in these processes.Footnote ³⁵ The ICJ’s 2004 decision in Avena, which was at issue in the Medellin litigation referenced above, is also an example of international law being construed to impose a domestic process requirement, namely judicial review of the convictions and sentences of certain individuals who had been imprisoned without proper consular notice,Footnote ³⁶ although the United States still has not implemented the requirement.

In addition to these horizontal separation of powers effects, international law may also affect vertical issues relating to federalism. In a variety of ways, international law tends to favor national over subnational control over foreign relations. For example, unless a treaty provides otherwise, it is deemed, as noted in article 29 of the Vienna Convention, to apply throughout the entire territory of a party. Similarly, under the international law of state responsibility, nations are viewed as responsible for the conduct of their territorial units, and they are not allowed to rely on their internal law, including internal law relating to federalism, as a justification for a failure to comply with their obligations.Footnote ³⁷ Although these presumptions in favor of national rather than subnational control of foreign relations law are understandable in a system of Westphalian nation-states, they can make it more difficult for constitutional values relating to federalism to be maintained, especially as international law increasingly overlaps with matters of traditional domestic regulation.

IV Conclusion

One of the virtues of studying foreign relations law, as noted at the outset of this chapter, is that it allows for an exploration of the rich and evolutionary relationship between foreign relations law and international law, a topic that has been under-explored in the literature. The present volume makes an important contribution in addressing that relationship from a range of perspectives, and it will undoubtedly spur additional scholarship on the topic. In addition to its scholarly value, the volume should be of interest to lawyers and policy-makers in both the domestic and international domains because it highlights how legal rules developed in one of these domains can have important, and not always beneficial, effects in the other.