In this important new book, Alex Mills, Slaughter and May Lecturer in Law at Selwyn College, Cambridge, marshals a grand historical narrative of the relationship between public and private international law and a detailed analysis of the constitutional dimensions of private international law in federal systems, in support of his case for a renewed ‘international systemic’ conception of private international law to service a coherent, ‘harmoniously pluralist’ international legal order.Footnote ¹

Mills' central argument is his claim that a rigid disciplinary separation between public and private international law sustains a flawed understanding of private international law as essentially municipal law, concerned with domestic notions of substantive justice and individual fairness. In place of this ‘conflict of laws’—a term the book uses in a pejorative sense—Mills proposes a conception of private international law that is systemic, international, public and constitutional in nature. It is systemic in its concern with the structure of the international legal order rather than with substantive results in individual cases. Its international character is claimed to inhere, not in its status as ‘really international law’ in the traditional sense of ‘not national’ law (this being a dichotomy that Mills rejects) but in the sense that it is ‘the embodiment of diverse, imperfect strategies which aspire to the universal value of reducing conflicts in the exercise of private law regulation’.Footnote ² It is public in its focus on effectuating an ordering of States' regulatory authority (in the field of private law), and constitutional, finally, in its insistence that this ordering be principled.

The project of the rehabilitation of an international systemic understanding of private international law begins with a historical analysis of the forgotten, or ‘private’, joint development of public and private international law as part of a ‘universal (natural) international law system … designed to address the problem of coordinating legal diversity’.Footnote ³ The separation of the two disciplines and the attendant conception of private international law as ‘necessarily and purely a part of national law’, Mills argues, was the product of the rise of legal positivism and of increased legal diversity, both in the late 19th century. This disciplinary compartmentalization has resulted in a persistent vision of private international law as reliant on an embarrassingly ambiguous concept of comity for its foundations, and as having the protection of private rights and interests for its aims.

Chapter 3, ‘From Positivism to Constitutionalism’ seeks to replace this positivist conception of the separation of public and private international law with an understanding of both fields as part of the same overarching ‘international constitutional’ framework for the ordering of regulatory authority. International constitutionalization, a process that Mills aims to both document and defend, is defined as the development of ‘a constitutional structure or architecture within which substantive norms can be recognized as having a certain value or effect based on the scope of the authority from which they are derived’.Footnote ⁴ ‘The reality is’, Mills claims, ‘that the international system is forming a constitutional global order, governed by emerging principles of public law’.Footnote ⁵ These emerging principles, qualified as secondary norms, or ‘norms of “meta-justice”’,Footnote ⁶ structure the demarcation of regulatory authority both as between States, and as between the national and international levels. The three main structuring principles Mills identifies are the ‘vertical’ ideas of the supremacy of international law (embodying the centralizing pull of the universal) and subsidiarity (recognizing diversity and pluralism), and the ‘horizontal’ concept of mutual recognition of regulation between States.

The implications for private international law of this systemic, ‘federalist’ perspective on the international legal order are explored throughout the remainder of the book in the form of an extended argument by way of analogy. Chapter 4 is built around an ingenious attempt to use federal constitutional legal ideas in support of not merely ‘a revitalization of the traditions of internationalism in private international law’,Footnote ⁷ but also as part of a broader attack on the dichotomies of public v private and international v national law themselves. Private international law in federal systems, Mills argues, contributes to the ordering of regulatory authority along horizontal and vertical lines. Using this grid to analyze the private international law systems of the United States, Australia, Canada and the European Union, Mills finds that in each of these settings, private international law rules are affected by their constitutional context, based on some form of recognition of the idea that these rules have a ‘systemic constitutional function’.Footnote ⁸ Chapter 5, finally, examines the relationship between public and private international law through an ‘international systemic’ lens, investigating the ways in which the systemic dimensions of structure and international rights protection are recognized and effectuated in both public and private international law. A central claim in this Chapter is that ‘private international law replicates ideas and debates about international ordering that are also reflected in public international law’.Footnote ⁹ ‘In reality’, Mills argues, ‘both public and private international lawyers are concerned, from different perspectives, with the same underlying principles governing the allocation of regulatory authority between states’.Footnote ¹⁰

Much of the argument in The Confluence of Public and Private International Law (Confluence) consists of the application of a federalism analogy at the international level. It is this idea that sustains the book's call for a systemic perspective on an international legal order comprised of both public and private international law, its search for principles of ‘meta-justice’ to govern this integrated international system, and the elaboration of detailed studies of the domestic—or regional—laws of federal systems in order to flesh out the operation of these principles. The federalism analogy, it is submitted, is the book's most distinctive contribution to the rich tradition of scholarship on the relationship between public and private international law. Mills himself, appropriately, cautions against overextending arguments by way of analogy.Footnote ¹¹ The international federalism analogy may, however, suffer from difficulties that go beyond this caveat.

A basic vulnerability of the international federalism analogy in Confluence, it is submitted, is its conflation of ‘international’ and ‘systemic’, of federalism and constitutionalism, and of ‘State’ and ‘substantive’. Mills' study is characterized by a determination to locate systemic ideas on the federal and international levels. At the same time, the book appears content with a view of local, State, legal orders as repositories merely of ‘substantive’ values, and without any significant systemic aspirations. These parallel moves, ironically, may ultimately undermine rather than support the book's powerful argument for a systemic perspective on private international law.

First, because in this conflated perspective the international level is seen as the primary locus for the operation of systemic ideas, Mills' argument is dependent on the availability of fairly thick constitutional principles on this global level. The search for these principles, in Chapter 3, however, has to negotiate all the familiar empirical, definitional and normative objections encountered in critiques of post-national constitutionalism.Footnote ¹² These objections are by no means insurmountable per se, but they do require lines of argument that Mills' study does not develop. Mills' discussion of the principle of subsidiarity, for example, relies heavily on the story of the development of this principle in the deeply peculiar historical and institutional setting of the EU. No sustained effort is made to show why this particular principle should be transposed to the global level, what such a process of ‘translation’ might look like in practice, or how the meaning of this principle might be affected by its new global surroundings.

Second, in its efforts to highlight the systemic dimension already inherent in the current international legal order, Confluence makes a broader case for the actual limiting effects of public international law doctrines on private international law than seems sustainable. While some such constraints undoubtedly exist, Mills' claim that current ‘public international norms … exert a fundamental influence over the development of private international law’ appears to go further than many private international lawyers would accept.Footnote ¹³

Thirdly, and most suggestively, the systemic/international conflation arguably leads Mills to gloss over an important aspect of the domestic federal law analogies he invokes—the fact that a number of the most high profile doctrines described are also applicable to international, i.e. extra-federal, cases. The ‘minimum contacts’ requirement in the US and the ‘real and substantial connection test’ in Canada, for example, apply both to inter-state, or inter-provincial, cases and to international cases. This basic commonality of application suggests that the normative foundations of these doctrines may have to be classified, at least in part, as ‘outward’ looking, local values and principles regarding the federation's position in the global legal order, rather than as merely ‘inward’ looking principles of federal organization. These underlying principles, in other words, while still clearly systemic and constitutional, are not necessarily predominantly federal in nature. By extension, following Mills' analogy, this suggests that the systemic principles organizing the international ordering of law need not themselves be primarily international.

Tellingly, the Supreme Court of Canada, in a cited passage from the Hunt v T & N case that could almost serve as the book's motto, once referred to ‘the confluence of private international and constitutional law’.Footnote ¹⁴ In the international context, however, constitutionalism in a systemic sense need not only refer to principles of federal constitutional architecture; it may also express individual communities' own commitments to their role in the international ordering of law. On that view, it does not matter whether these communities are federations or not, although federations may of course have more experience with the types of problem involved.

This idea of local—not federal or international—constitutionalism as a guiding force for private international law has some attractions. It does not, for example, depend on the availability of thick normative surroundings on a global level. It is also not as easily undermined by the absence of strong public international limitations on conflicts doctrines. Of course this alternative perspective and the contrast it represents with Mills' approach, require some nuance. Some of the doctrines Mills discusses, for example, do treat the difference between domestic and international cases as one relevant factor among others. And some of the systemic principles identified cannot be seen as either purely local or federal in nature, but as examples of an intermediate category of norms. Overall, though, through its conflation of constitutionalism and federalism, Mills' approach arguably misses out on some of the international systemic potential of local constitutional ideas.

Confluence states that its primary aim is to effectuate a ‘change of consciousness concerning private international law, through the adoption of an international systemic perspective’.Footnote ¹⁵ In keeping with this aim, and given the vast range of material covered simply to support the argument, it is entirely understandable that the book gives only few indications of the practical consequences the adoption of such a perspective might entail. But especially when taken as a sustained argument for a systemic perspective on the international legal order, even when that perspective might be somewhat less ‘federal’ than Mills suggests, and as a call for all international lawyers to update their analogical references from private to public, The Confluence of Public and Private International Law is an impressive and very welcome scholarly contribution.