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.

I Populism, Constitutional Law’s External Face and International Law

The choices that states make about how their internal constitutional systems relate to the world outside – the international – are not accidental. They reflect fundamental decisions about how open or closed the state is to international lawFootnote ¹ and about the level at which governance decisions that affect societies are made. Despite this, the legal relationship between the domestic and the international is under-theorised. It has been characterised by a ‘dichotomy [which] remains perhaps the least investigated of all the fundamental divisions in our political lives’.Footnote ²

The fissure between the municipal and the international has been exposed to view – and exploited – by the contemporary rise of so-called ‘populism’ in many states. A key tenet of populism has been a form of exclusionary identity politics that, mobilising popular sovereignty, creates a division between ‘the people’ and the other, seen in Hobbesian terms as the enemy outside.Footnote ³ Populism makes a claim to sociological legitimacy – that society should not be controlled by external forces – that leads to a turn against ‘elites, supranational agreements, international judicial institutions or economic powers’.Footnote ⁴ The result is a context in which ‘international law is invoked, but in what seems an increasingly antagonistic way, amounting often to a dialogue of the deaf’.Footnote ⁵

Despite the central importance of the external face of populism, surprisingly little attention has been paid to its legal significance, in comparison to its internal constitutional implications.Footnote ⁶ The populist challenge to international law is particularly concerned with the boundary between the international and the domestic, in which national sovereignty – linked with the popular sovereignty of ‘the people’ – is invoked as the key concept. In legal terms, this means that the challenge presented by the external face of populism is not only about the way in which states interact on the plane of international law, in the discourse between states and in their engagement with and within international institutions. It is also, perhaps even principally, about the relation between the internal law and institutions of the state on the one hand and international law on the other. This is the domain of foreign relations law.

The result is that the renewed attention given to foreign relations law as a field of comparative study (and not merely an American Sonderweg)Footnote ⁷ comes at a time when the legal doctrines are being tested and debated to an unprecedented extent in many states in ways that expose to view the underlying policies and principles served by the law in this area. Yet this is not only a linear story about the enlargement of executive power fuelled by popular mandate. In constitutional democracies, it also is an account of the ways in which the other organs of government, the legislature and the courts, articulate their own role.

The publication of the present collection of chapters – the fruit of a well-conceived symposium – therefore presents an opportunity to reflect on the manner in which foreign relations law mediates the relation between the domestic and the international legal realms at a time when this is a hotly contested boundary. This is not simply an exercise in comparing legal techniques. Rather, it invites consideration of a larger question: what is foreign relations law for?

It is possible to examine that question (as I have done elsewhere) as one of the perspective or conception of the function of foreign relations law with which the field is approached.Footnote ⁸ Seen in this way, both the scope of the field and the development of specific legal doctrines will be affected by whether foreign relations law is conceived as designed to maintain the exclusion of the international from the domestic realm; or alternatively to facilitate the reception of international law into the domestic sphere. It may bring the conduct of foreign relations within the domestic constitutional sphere or concern itself with the external conduct of diplomatic relations between states. Finally, it might be reconceived as a conflict of laws for public law, performing an allocative function on questions of jurisdiction and applicable law as they arise in the external exercise of public power. In this latter perspective, the field draws upon elements of public and private international law as well as constitutional law, even if (like private international law itself) it must always remain a part of the domestic law of each state.

This book shines a specific spotlight on the relationship between comparative foreign relations law and public international law. Amidst what Edward Swaine describes as ‘the considerable, and understandable, excitement regarding the nascent field of comparative foreign relations law’,Footnote ⁹ it is worth pausing to ask what implications this might have for the development of international law itself. Is the turn to foreign relations law, as Anthea Roberts has suggested, ‘an inherently conservative move’?Footnote ¹⁰ After all, foreign relations law had been until recently hardly recognised as a field outside the United States. There it has taken a pronounced inward turn in the most recent generation of scholarship. Is it not more than coincidental that it should be exported as a comparative field at a time when the rise of populism, in the United States and elsewhere, increasingly resists the role of the international in the domestic polity?

What effect might the development of comparative foreign relations law as a field have on public international law itself? Helmut Aust and Thomas Kleinlein argue in their Introduction that ‘it is precisely this by now established narrative of an “Ersatz international law” that should be challenged critically’.Footnote ¹¹ But in order to do so, it is first necessary to consider that narrative. Section II will enquire whether, and if so how, an increased focus on foreign relations law might itself undermine international law or create an ‘Ersatz international law’.

The balance of this chapter considers two lines of response. Its central argument is that a renewed focus on the relation between international law and foreign relations law, which the present collection adopts, might in fact address such a critique.

Section III argues that, once the more extreme rhetoric of the populist critique of international law is stripped away, the debate exposes to view the importance of reconnecting the external and internal aspects of sovereignty. Populist leaders have adopted (and often appropriated for their own purposes) a much more deep-seated and genuine concern about the exercise of popular sovereignty vis-à-vis governance at the global level, which should not be dismissed. Brexit is emblematic of the reignition of a much larger and critically important debate about how ‘the people’ of a nation are to determine the manner in which they are to engage with the world. This is not a new issue, though it has been sharply re-exposed to view in the present era. In this debate, there is no necessary dissonance between international law – which retains as a peremptory norm the principle of self-determinationFootnote ¹² – and the viability of a national constitution founded on representative democracy. On the contrary, it is the populist claim of an exclusive executive right to speak for the people in foreign relations that we should question.

Section IV then suggests a second important line of response. This is precisely that recognising the concerns of foreign relations law to be legal concerns (as opposed to the exercise of executive discretion in a zone of non-law) enables consideration of the interaction between the domestic constitution and international law as one concerned with the interaction of legal systems. In other words, it necessitates treating international law as law and the domain of foreign relations as not being purely political but as bounded by law. This is not about treating all exercises of foreign policy as constrained by law, still less as necessarily subject to domestic adjudication. Rather it requires us to take seriously the extent to which the executive foreign affairs function is bound by the international law obligations that it assumes on behalf of the state.

The diverse chapters collected in the present volume cast important light on a set of legal questions that arise out of a governance dilemma that many states now face with increasing urgency. It may well be impossible, as Dani Rodrik has suggested, to have ‘hyperglobalization, democracy and self-determination all at once’.Footnote ¹³ But, even if we put aside ‘hyperglobalisation’, we must still find a way to reconcile popular engagement in the process of government at the national level with the necessity of international cooperation.

II An Ersatz International Law?

In order to challenge critically the idea that foreign relations law is a kind of Ersatz international law, as the editors of this volume invite us to do, it is first necessary to examine the nature of the charge. How might it be said that the emergence of foreign relations law, as a discipline on a global comparative scale, could adversely affect international law itself? Here experience in the United States, as the country in which foreign relations law as a distinct subject has the greatest prominence, may be instructive.

In an important contribution to the debate about the emergence of the field of comparative foreign relations law, Karen Knop identifies three anxieties about the effect of the creation of such a field on public international law itself in light of the American experience.Footnote ¹⁴ In the first place, she notes that the study of foreign relations law has displaced international law in many American law schools, with the consequence that students are ‘less likely to approach public international law as a legal system than instrumentally as one possible tool in the legal toolkit for solving transnational problems’.Footnote ¹⁵ In the second place, she suggests that foreign relations law may end up taking dualism to its ultimate end. This ‘deep dualism’Footnote ¹⁶ discounts the legal quality of international law, such that ‘the field of foreign relations law is structured as a divide between an internal realm in which law is the default and an external realm in which foreign relations is the default’.Footnote ¹⁷ In the third place, she identifies the risk that foreign relations law distorts the operation of international law: by inserting domestic concerns into the operation of international law; by encouraging non-compliance with international law at the national level, inserting boundaries derived from domestic constitutional law; or by opening the potential that domestic courts will simply misconstrue its obligations.

These concerns cannot be ignored, at least insofar as they are observable in the contemporary American context. Jens Ohlin argues in his book The Assault on International Law that the development of doctrines in US constitutional law that enhance executive discretion in foreign relations went hand-in-hand with scholarship that sought to undermine the determinate and binding character of international law.Footnote ¹⁸

Recent experience also exposes the risk of blurring important lines of distinction between the operation of international and national law. Naz Modirzadeh describes how, after 9/11, international humanitarian law became ‘at best a set of tools that could be operationalized alongside constitutional law, human rights law, and criminal law and procedure’ in a form of ‘folk international law’.Footnote ¹⁹

Nor are these trends limited to the United States. John Finnis, arguing that the executive in the United Kingdom has no obligation to abide by the state’s international law obligations, writes: ‘International law remains, like it or not, a defective example of law. The criteria for its formation and identification remain opaque, controverted, and manipulable without redress’.Footnote ²⁰

Chapters in this volume bear out some of the concerns that Knop identifies. Felix Lange shows how the insertion of the domestic constitutional law limitations of the United States into the negotiations shaped the outcome of the Paris Agreement on climate change at the international level, while providing no subsequent constraint on the executive decision to withdraw at the domestic level.Footnote ²¹

Foreign relations law may also encourage the priority of constitutional law concerns over international law obligations. Angelo Golia recounts the refusal of the Italian Constitutional Court to give effect to the judgment of the International Court of Justice in the dispute between Germany and Italy on sovereign immunity for acts committed in World War II, in which it cited supreme principles of the constitution.Footnote ²² As Curt Bradley observes, ‘the normative goals of foreign relations law will not always align with the normative goals of international law’.Footnote ²³

A closer embrace of international law at the national law level may also lead to its misapplication. Dire Tladi argues in his critique of the South African Constitutional Court judgment in the SADC Tribunal case that ‘the problem with the Court is not only its conclusion but also its failure to engage with the methodology of international law’.Footnote ²⁴

To these concerns, the rise of populism adds the prospect of an increasing outright withdrawal of states from the international legal system, facilitated by the exercise of an unbound executive discretion to withdraw within many domestic constitutions.Footnote ²⁵ This is a trend of which President Trump’s announced withdrawals from the Paris Agreement and the Iran Nuclear Accord – both so recently and painstakingly negotiated – are emblematic. Yet the evidence of withdrawal, in particular from submission to international dispute settlement, is in fact much more widespread.Footnote ²⁶ Examples include the United Kingdom’s withdrawal from the jurisdiction of the European Court of Justice under Brexit; the increasing challenge to the jurisdiction of the European Court of Human Rights; the threatened collective withdrawal of African states from the International Criminal Court; and the withdrawal of a number of key states from investment treaty arbitration.Footnote ²⁷ In each case, there is a striking similarity in one of the key strands in the arguments for withdrawal. Those objecting to the conferral of a power of adjudication over states upon international tribunals allege that this creates a democratic deficit. International judges, described as unaccountable international elites, are said to take decisions that constrain the power of peoples to exercise their popular sovereignty by determining the direction of their societies for themselves. They assert that this undermines the essence of the sovereignty of states.

International law has seemed curiously impotent in the face of these newly emboldened assertions of sovereignty, though I have argued elsewhere that international law does place checks on withdrawal, recognising that it is an act that is not a matter of purely unilateral discretion, since of its nature it affects the interests of other states parties.Footnote ²⁸ The question that this phenomenon raises in the present context is whether a closer engagement between international law and foreign relations law is capable of nourishing new insights into the concept of sovereignty in its double-facing aspect: external and internal.Footnote ²⁹ Such a constructive engagement might furnish one possible set of responses to the critique outlined above. It is to this question that we must now turn.

III Is Sovereignty Indivisible?

Modern international lawyers have a tendency to regard the sovereignty of states as something of an embarrassment – an inconvenient truth. In the last edition of Oppenheim that he edited in 1955, Hersch Lauterpacht concludes a passage on ‘The problem of sovereignty in the twentieth century’ with the optimistic suggestion that ‘progress in International Law, the maintenance of international peace and, with it, of independent national States, are in the long run conditioned by a partial surrender of their sovereignty’.Footnote ³⁰ Forty years later, Louis Henkin concluded in 1995 that ‘for legal purposes at least, we might do well to relegate the term sovereignty to the shelf of history as a relic from an earlier era’.Footnote ³¹ James Crawford insists in 2005 that the term sovereignty as a legal term can only mean ‘the totality of powers that States may have under international law. By contrast, as a political term its connotations are those of untrammelled authority and power and it is in such discourse that the term can be problematic’.Footnote ³²

The view of international lawyers that sovereignty is unhelpful in legal terms stands in stark contrast to its persistence. This is not only in international political discourse, in which, for instance, Brexit was cast as ‘a fight for the very sovereignty of our nation’;Footnote ³³ and President Trump repeatedly invoked at the rostrum of the UN General Assembly the notion that: ‘The future does not belong to globalists. The future belongs to patriots. The future belongs to sovereign and independent nations …’.Footnote ³⁴ It also finds its way into international legal discourse. The Beijing Declaration adopted by the first South-South Human Rights Forum in 2017 resolves that: ‘The international community’s concern for human rights matters should always follow international law and the universally recognized basic norms governing international relations, of which the key is to respect national sovereignty’.Footnote ³⁵ So too the proposal for collective withdrawal from the International Criminal Court considered by an Open-ended Ministerial Committee of the African Union in January 2017, invoked the need to ‘[p]reserve the dignity, sovereignty and integrity of Member States’.Footnote ³⁶

The comparative failure of international lawyers to engage with the concept of sovereignty, in both its internal and external aspects, may, as John Jackson presciently warned in 2003, actually promote the persistence of sovereignty fictions such as ‘the notion that absolute power is concentrated at the head of a nation-state’. Jackson argued that an attempt to bury the concepts of sovereignty ‘without adequate replacements could lead to a situation in which pure power prevails: that, in turn, could foster chaos, misunderstanding, and conflict, like Hobbes’ state of nature, where life is “nasty, brutish, and short”’.Footnote ³⁷

Jackson was writing at a time of great expansion in the ambition of international institutions and was driven by a perception of the entirely new set of pressures that this was creating for ‘nation-state governments trying to deliver the fruits of their important achievements to their constituents’.Footnote ³⁸ In other words, he was concerned about the effect of exercises of sovereignty on the plane of international law on the maintenance of popular sovereignty in national constitutions. Seen in this light, the rise of populism has simply exposed to view what Blokker calls a ‘deeper, intrinsic tension in the post-war international legal order between democratic self-government on the one hand, and a universalistically understood international regime, on the other’.Footnote ³⁹

This is a serious concern that lies at the heart of several of the chapters in this volume. It is not to be dismissed as mere populist rhetoric. Aust and Kleinlein suggest in their Introduction that ‘Sovereignty often serves as a placeholder for constitutional values, in particular domestic democratic self-determination’.Footnote ⁴⁰ As Anna Petrig puts it, discussing the Swiss constitutional debate about the Migration Pact: ‘To shrug off the call for “hard participation”, which took shape in the context of the Migration Pact, as a purely populist manoeuvre would not do the matter justice’.Footnote ⁴¹

International law resists conflating the question of the sovereignty of a state on the international plane with the ‘constitutional lawyer’s question of supreme competence within a particular State’.Footnote ⁴² At the same time, there is a strong strain in foreign relations law, which finds its philosophical origins in John Locke’s idea of the ‘federative power’ that would leave the conduct of foreign relations in the hands of the executive.Footnote ⁴³ On the face of it, these two claims seem to contradict rather directly the notion, now so widely exploited by the populist leaders, of the importance of a direct link between ‘the people’ and the exercise of independent sovereignty on the international plane, for which the Brexit referendum is emblematic.

Yet a closer focus on the relation between the international and the domestic dimensions of sovereignty and on the contribution of, respectively, international law and constitutional law might assist our understanding of this relationship. In his highly original monograph Sovereignty published in 1933, Hermann Heller argued for the indivisibility of sovereignty. He wrote:

In his view, it was essential to liberate the idea of the sovereign person from the ‘bloodlessness’ of a ‘conceptual phantom labelled the state’.Footnote ⁴⁵ He located sovereignty in the people as the body politic, but, distancing himself from Carl Schmitt’s conception of a ‘voluntaristic dictatorship’ he insisted that the people may only govern through the appointment of representatives ‘juristically dependant magistrates’ that represent the common will.Footnote ⁴⁶

Several of the chapters in this volume examine the development of mechanisms that seek to enhance and protect democratic involvement in the decisions of states on the international plane, which comparative research shows is a global trend.Footnote ⁴⁷ Both Ajla Škrbić and Stanislaw Biernat consider the case for an enlarged parliamentary role in controlling the executive’s use of the foreign affairs power.Footnote ⁴⁸ Niki Aloupi shows how the Conseil Constitutionnel in France mediates the effect of international commitments upon national sovereignty, through its decisions on whether a constitutional amendment is required as a condition for the ratification of a treaty.Footnote ⁴⁹

Veronika Fikfak, who considers the development of British parliamentary practice on the use of force against the background of a much broader comparative trend, argues that this development is not only about the accountability of the executive to Parliament. Examining the parliamentary debates, she suggests that, in the process, a direct link has been forged between the questions of the lawful use of force at international law and Parliament’s responsibility at the national level to decide to authorise the use of force.Footnote ⁵⁰ In the process, the international law issues become domesticated.

These trends, important though they are, still fall short of Heller’s conception of indivisible sovereignty through the exercise of the ultimate power of decision on foreign affairs by the elected representatives of the people. Nevertheless, recent experience in the United Kingdom concerning the decision to withdraw from the European Union gives support to this idea. Brexit concerned an exercise of the foreign affairs power: the decision to withdraw from a Treaty (and the whole complex of international arrangements that flow from it). The process in the United Kingdom began with that most un-British of constitutional devices: a resort to direct popular democracy through the medium of a referendum. Immediately thereafter the executive (vociferously backed by elements in the Press) attempted to treat this as a mandate that could be executed by a straightforward exercise of its foreign affairs prerogative.Footnote ⁵¹

In two landmark cases, the Supreme Court demurred, decisively finding in favour of Parliamentary sovereignty, that is: the principle that the sovereignty of the people may only be exercised through their representatives (however chaotic the results may be) and that this principle applies as much to foreign relations as it does in other spheres. The first case directly concerned the decision to notify withdrawal. The second concerned a decision to prorogue Parliament while withdrawal negotiations were ongoing.

In Miller (No. 1),Footnote ⁵² the Court rested its decision on the ground that the decision of the executive to withdraw would necessarily change the law applicable within the United Kingdom, something that only Parliament was competent to do. In this way, the Court could present the outcome as upholding the ‘dualist system’ that separated the international from the national and in turn the executive foreign affairs function from the legislative function of Parliament. It was only because the nature of withdrawal from EU law necessarily transgressed that line that the court had to intervene, since ‘the dualist system is a necessary corollary of Parliamentary sovereignty … it exists to protect Parliament not ministers’.Footnote ⁵³

In Miller (No. 2),Footnote ⁵⁴ however, the issue could not be analysed as an application of dualism in law-making. The Court recognised that what was really at stake in the prorogation of Parliament was not merely an internal question of the distribution of powers between the executive and Parliament, but also one that went to the heart of Parliament’s ability to scrutinise the executive conduct of foreign affairs. The constitutional significance of that power of supervision was one that Dicey early identified. He accepted that ‘it is not Parliament but the Ministry, who direct the diplomacy of the nation’.Footnote ⁵⁵ At the same time, Ministers were constantly accountable to the House of Commons for the exercise of that power. In this way, he thought ‘The prerogatives of the Crown have become the privileges of the people’.Footnote ⁵⁶ For the Supreme Court, the principle of ‘Parliamentary accountability’ is ‘no less fundamental to our constitution than Parliamentary sovereignty’ since: ‘By these means, the policies of the executive are subjected to consideration by the representatives of the electorate, the executive is required to report, explain and defend its actions, and citizens are protected from the arbitrary exercise of executive power’.Footnote ⁵⁷

Does this mean that the sovereignty of Parliament now includes the sovereign power of decision on all matters of foreign affairs? The answer is still probably not: the gradual increase in Parliamentary supervision of treaty-making and the growth of a convention with regard to prior consultation on the war power do not amount to a full assumption of power. Nor would this be consistent with the important value of the separation of powers in constitutional government that requires a balance to be maintained between the three organs of government. Nevertheless, the ‘crisis’ test that Heller invites us to apply has demonstrated, at least in this one contemporary example, the need in the last resort to find a single holder of sovereign power within the state. Within a democratic state, that holder can only be the constitutionally appointed representatives of the people.

How, then, can this domestic constitutional law point be connected with international law in a way that supports the idea of an indivisible sovereignty? The answer lies in one of the most central organising principles of the post-War system of international law: the principle of self-determination.

The principle is enshrined in the United Nations Charter as one of the principal purposes of the Organisation, being ‘respect for the principle of equal rights and the self-determination of peoples’.Footnote ⁵⁸ It has been subsequently developed through law-making resolutions of the General Assembly on Colonial PeoplesFootnote ⁵⁹ and on Friendly RelationsFootnote ⁶⁰ and as the first human right in the International Covenants.Footnote ⁶¹ In the latter, in common article 1, it finds its expression in the following way:

1. (1) All peoples have the right to self-determination; by virtue of that right they freely determine their political status and freely pursue their economic, social and cultural development.

2. (2) All peoples may, for their own ends, freely dispose of their natural wealth and resources without prejudice to any obligations arising out of international economic co-operation, based on the principle of mutual benefit, and international law. In no case may a people be deprived of its own means of subsistence.

3. (3) The States Parties to the present Convention, including those having responsibility for the administration of Non-Self-Governing and Trust Territories, shall promote the realization of the right to self-determination and shall respect that right, in conformity with the provisions of the Charter of the United Nations.

In turn it has been developed and implemented through the practice of the United Nations. No single principle has more profoundly transformed the international legal system.Footnote ⁶² Respect for it as ‘one of the essential principles of contemporary international law’Footnote ⁶³ is an obligation erga omnes, which all states have a legal interest in protecting.Footnote ⁶⁴

The point here is that the self-determination creates an explicit link between international law and the ‘people’ who are and remain the holders of the right.Footnote ⁶⁵ Self-determination as a legal principle has both driven the emergence of new States and limited the validity of attempts to create new states that do not meet its criteria. But for present purposes, its significance lies in its enduring application internally within the framework of an existing state.Footnote ⁶⁶ In this way, international law supports the essential connection between the internal and the international role of self-determination: between the people and their right to determine their political organisation. So, renewed attention to the connection between international law and foreign relations law may shed new light on the meaning of popular sovereignty and its relation to the right to self-determination.

This point is important because the international law principle of self-determination is no populist charter, licensing the will of the majority to the exclusion of the human rights of individuals. Its expression as a matter of customary international law in the Friendly Relations Declaration includes the provision that: ‘Every State has the duty to promote through joint and separate action universal respect for and observance of human rights and fundamental freedoms in accordance with the Charter’.Footnote ⁶⁷ The same principle adds, in its savings clause, that the consequence of due observance of the principle of equal rights and self-determination of peoples is that the State is ‘thus possessed of a government representing the whole people belonging to the territory without distinction as to race, creed or colour’.Footnote ⁶⁸ The insertion of the right in the international human rights covenants has the same consequence that it is to be read together with all of the other rights protected thereunder.

There is a second respect in which a focus on the relationship between international law and foreign relations law may also prove productive. That lies in treating seriously its starting premise: that international law constitutes a distinct legal system, and that part of the function that foreign relations law may perform within a domestic legal system is to provide rules of reception, or, put more broadly, rules that manage the interaction between legal systems by determining which legal system has jurisdiction over which issues and what law applies. It is to this aspect that we must now turn.

IV International Law As Law

In their Introduction, Aust and Kleinlein reject the idea that international law or foreign relations law are ‘hybrid in nature’. They seek to uphold ‘the rather traditional view that international law is indeed international and that foreign relations law is part of a given domestic legal system’. Nevertheless, they argue that ‘foreign relations law encapsulates the rules of domestic law about the reception of international law’ and that ‘upholding the traditional criteria … does not preclude investigating the hybrid zone that is created by the encounters of public international law and foreign relations law’.Footnote ⁶⁹

This approach may provide a potential way of pursuing Knop’s suggestion that ‘[o]ne way forward may lie in noticing and questioning the strong law/politics distinction at play in both foreign relations law and the international law that it threatens to displace, discount, or distort’.Footnote ⁷⁰ In other words, it may answer the distinction – implicit or explicit in some contemporary foreign relations law scholarship – between a relatively positivist approach to binding law at the domestic constitutional level and the assumption that, beyond the state, the international arena can be characterised only by foreign relations and not by binding law.

The partially revised American Law Institute Restatement (Fourth) Foreign Relations Law 2018 makes the point that, because a restatement of foreign relations law ‘deals with two distinct legal systems, namely domestic law bearing on foreign relations and relevant portions of international law, it must address both’.Footnote ⁷¹

How might a renewed focus on treating the interface between international law and domestic constitutional law as one of the interaction between legal systems actually make a difference? In the first place, it might challenge the utility of conventional ways of analysing the reception of international law in domestic legal systems as one determined by the distinction between dualist and monist systems. Recent comparative research has shown that this traditional distinction does not correctly explain the actual rules of recognition applicable in states that are traditionally regarded as being ‘monist’ or ‘dualist’.Footnote ⁷² The true position is much less black and white.

‘Monist’ states must still maintain procedures for treaty review and ratification to ensure legislative control over the making of laws that are to be applicable internally within the state. ‘Dualist’ states, even if they maintain strict rules of separation between treaty obligations and domestic law may still accept that customary international law is ‘part of the law of the land’.Footnote ⁷³ When they do so, this is not because international law is referred to in the interpretation of a norm of municipal law. Rather it is because international law is applicable to the determination of the issue within the municipal legal system. It is applicable because a rule of recognition of municipal law so provides, and therefore subject to the terms on which municipal law admits the international law rule. But it is nevertheless applicable as law.Footnote ⁷⁴

A consideration of the internal effect of the international legal obligations assumed by states might also lead us to question deep dualism in another respect. It would challenge another mistaken dualist proposition that international law obligations sound only on the international plane and produce no domestic effects. It would do so by demonstrating that the essential corollary of the allocation to the executive of the power to conduct foreign affairs and to enter into treaties is that the executive assumes a concomitant obligation to comply with the international law obligations that it has assumed. Such a requirement (which is supported in the case of the United Kingdom by several centuries of practice) ensures that the state abides by the international law obligations that it has assumed through the persons that contract on its behalf and represent it in foreign relations.Footnote ⁷⁵

The result of treating foreign relations law as concerned with the interaction of the different legal systems that are in play in questions of foreign relations ‘admits of a larger variety of relevant bodies of law. It also has the potential to develop a more complex account of dualism’.Footnote ⁷⁶ In rejecting a ‘fixed law/politics opposition’ it would subject foreign relations questions to the principle of legality, not conceived narrowly as the municipal law of any particular state, but rather as determining the issue according to the applicable law, whether that be municipal law or international law.

A further benefit of such a focus is that it may provide a better means of doing comparative foreign relations law on a global basis. Michael Riegner, in his chapter for this volume, highlights the contingency of the set of choices for foreign relations law created by the Western constitutional tradition.Footnote ⁷⁷ He points out that this tradition assumes the pre-existence of the state and then poses the foreign relations law question as a set of choices about the relation of the state to international law at the interface. He argues that ‘the distinction between international and national is applied rigidly to the political sphere but not to the economic sphere’.Footnote ⁷⁸

By contrast, in the colonised Third World, ‘foreign relations did not begin as inter-state relations but as dealings between chartered trading companies like the East India Company and local rulers. The experience of statehood was also quite different: for many postcolonial states, the international preceded the national: peripheral statehood was produced and defined by international law during decolonization’.Footnote ⁷⁹ A search for models of foreign relations law in the Global South would, as the Latin American example that he discusses illustrates, open up the possibility of transformational constitutionalism, a model of regional integration that emphasises social not economic rights, which remain much more closely subject to national control.Footnote ⁸⁰ We might note in this regard how closely the formulation of the right to self-determination in Article 1 of the International Covenants links the right of peoples to determine political status (paragraph 1) to their right to control economic resources (paragraph 2).

V Conclusion

If comparative foreign relations law proves itself really capable of embracing different perspectives as to the relation between a national constitution and international law that treats both as law, it might rise above a mere comparison of differences. It might then dispel the concern that, as a discipline, it may cannibalise the study of international law, creating in the process an Ersatz or ‘folk’ international law. In doing so it may shed new positive light on a compelling issue of our age on which foreign relations law sits, whether as bridge or boundary, namely: how to redefine the relation between the nation state and the international realm in ways that give real meaning to both the right of peoples to self-determination and the community interest shared by all humanity to secure our common future.