Different people write about the history of international law differently and for different reasons, inspired by the wish to put their international historical legal scholarship at the service of different causes. Some approach this study with a sense of moral duty to those whom the promise of international law has left betrayed or ignored and who are hopelessly wondering what international law’s wrong turn or inaction has practically to do with their current dismal fate. On other occasions, international legal history is approached as part of an effort at international legal norm-entrepreneurship with a view to reforming a specific element in the international legal order with a statistically proven ability to save lives or reduce the likelihood of harm if they are faithfully complied with. In other cases, international legal history serves to trace parallelisms between past scenarios and present-day concerns in order to tailor, through trial and error, better policy choices than those delivered by the earlier adoption of a particular international legal course rather than other alternatives. At other times, thinking backwards and forwards in time may help one to see with greater acuity what particular style of scholarly treatment a subject deserves in order to render justice to the victims of past abuses, for impending crises to be timely deactivated, or for ongoing global threats to be handled in the most constructive and orderly possible manner. Sometimes, retrieving the historical memory of international law contributes to raising consciousness of the root causes underlying certain recurrent phenomena of international concern while catering for the intellectual and ethical betterment – although these two do not necessarily follow each other – of its contemporary protagonists in the light of less than edifying examples of some of their predecessors. While referring to different themes of historical investigation and making use of a diversity of historical methods, many of these and many other uses of historical research in international law perform a critical function. This is because by delving into the rich reservoir of accumulated – but never unequivocal – knowledge of international law that the past has bequeathed to us they intend to elicit, to different degrees and on different scales, a change or transformation in the present status quo inspired by an esprit critique d’internationalité.

One may agree with Martti Koskenniemi that ‘much of the recent surge of interest in the history of international law has been fed by postcolonial attitudes in the legal academy’. The rise of post-colonial international legal historiography ensued logically from the fact that between the end of World War II and the fall of the Berlin Wall alone eighty-nine colonies reached sovereign independence: eleven in the first five years after the end of World War II; eight in the 1950s; forty-four in the 1960s; twenty-four in the 1970s; and two in the 1980s. Originally spurred by decolonization, in recent years this historiographical trend has been further favoured by globalization and the shift towards a multipolar world.

Writing some years ago, in an early phase in the so-called turn to the history of international law, Martti Koskenniemi noted that ‘there has been virtually no attempt to study international law from the perspective of the sociology of the international system’ and that the ‘possibilities for a historical sociology of international law are, in fact, almost limitless’. Since then, the history of international law has become more inclusive in its narratives of the multiplicity of social contexts and the social actors that have been shaping international law as a historical social product and of the moulding effects of the latter on the global society following Clifford Geertz, for whom all law is ‘constructive of social realities rather than merely reflective of them’. In good proportion, this historiographical development mirrors the extent to which state-centrism has lost some of its traditional paradigmatic position in international legal scholarship as a result of the relative decline or demise of the sovereign state as the main actor – and, classically, also the sole legal subject – of the international legal order.

International law is a result of the past and yet its history is being constantly reshaped in the image of contemporary times. This is so because all histories written about the past are invariably conditioned by the tendency, of which no historical work is absolutely free, to look at past events, actors, institutions, processes, and texts through the lenses of contemporary values, concepts, and circumstances. These new histories, which rethink the past in the present, influence our perception of contemporary matters in international law and also inform our understandings of how they may potentially unfold. However, while all historical research plays a performative narrative function, with a hidden potential to shape both contemporary and future events, this potential is particularly acute in international law, understood as the living legal system of a globally diverse international community of states and peoples. It is in this, albeit partial, sense that every epoch remakes the history of international law in its own image.

Since what has come to be known as the turn to the history of international law, international lawyers writing about international legal history have been partially freed from the pressing need to justify their research on the past of international law by referring to the present normative evolution of their field or its practical doctrinal utility in contemporary international legal debates. The gradual carving out of a sub-disciplinary and relatively self-contained academic space for international legal historical scholarship proprio sensu has been complemented by a closer attention to historical methods imported into the field by international lawyers or exported into it by scholars contributing from adjacent disciplines, namely legal historians and historians. The resulting interdisciplinarization of international legal history has prompted a series of methodological and historiographical debates around the distinction between two main ways of approaching it: those of historians and those of international lawyers. The first of these are allegedly concerned with guaranteeing a ‘well-contextualised historical record of the past for its own sake’, while the second have been described as being ‘mostly interested in the international legal afterglow of past events’.

Whether it is in terms of standard-setting, international law-making, international adjudication, or international enforcement of international norms, global, regional, and operationally conceived international institutions and organizations have become fundamental actors in the great contemporary world theatre where the drama of international law is constantly being re-staged. International institutions and organizations (IOs) are ‘frequently, if not exclusively’ terminologically equated with ‘intergovernmental organizations’, which are defined as ‘organization[s] established by a treaty or other instrument governed by international law and possessing [their] own international legal personality’ that ‘may include as members, in addition to states, other entities’. Although IOs have had a number of both practical and intellectual historical forerunners since the Central Commission for Navigation on the Rhine, which is usually considered the first IO, was set up in 1815, the reach of IOs has expanded exponentially through multiple functional international areas to reach an estimated number of over 350 worldwide today.

The lives, works, and times of international lawyers, thinkers, and scholars, who during their careers may often interchangeably play the roles of international judges, diplomats, or legal advisors to states, international institutions, transnational corporations, or non-governmental organizations, broadly constitute the scope of biographical approaches to the history of international law. A methodologically revamped turn to the cultivation of international ‘legal biography’ has been one of the characteristic features of the turn to the history of international law. Although reconstruction of the lives, works, and times of prominent international lawyers has long been a sub-genre in international legal scholarship, such lawyers and scholars have never been the object, apart from a very few limited exceptions, of professional historical biographical studies in the guise of those devoted to great statesmen or famous artists. The new wave of biographical approaches to the history of international law is thus characterized by a greater stress on the use of a ‘biographical tone’ and by more detailed attention to the political, intellectual, and professional contexts within which intellectually biographed international lawyers have contributed to the discipline over time. The turn to international legal biography has also encompassed a far greater coverage of the dramatis personae of the history of international law than was provided by earlier biographical accounts. The treatment they are currently receiving is, furthermore, more clearly influenced by the far larger diversity of animus historiandi underlying contemporary developments in historiography than hitherto in international legal history.

In its post-2000s expansion, the history of international law has more openly embraced the interdisciplinary pollination of a research field that blends international relations theory and its historical discourse, legal history, the history of ideas and political thought, and history writ large with the history of international legal practice and theory. It is being currently cultivated by a heterogeneous group of scholars made up of international lawyers occasionally transmuted into amateur historians; legal historians sporadically struggling to present themselves as savvy international lawyers; historians of international political thought sometimes posing as all the aforementioned; and, occasionally too, professional historians, who, as Andrew Fitzmaurice notes, are increasingly ‘engaging with the subject as part of their turn to the international dimension of history’. The disciplinary boundaries of international legal history have correspondingly become more fruitfully porous to a number of adjacent academic disciplines which, like international law itself, have also been significantly impacted by globalization and, in its wake, by the decrease in the intellectual leverage of ‘methodological nationalism’ which the professional birth of the academic disciplines of both law and history were born tied to in the late nineteenth century.

The thematic expansion and methodological sophistication experienced by historical writing about international law has greatly enriched contemporary international legal scholarship. Up to a point it has also prompted the intellectual emancipation of international legal history, which until not long ago was considered to be ‘a singularly underprivileged field of studies’ as a semi-autonomous and relatively self-contained research area. This is not a minor intellectual development in itself and neither one without significance for the discipline as a whole to continue evolving, as Jürgen Habermas would put it, from ‘a flexible medium for shifting constellations of power’ towards ‘a crucible in which quasi-natural power relations could be dissolved.

The academically popular catchphrase ‘the turn to history in international law’ is often used to broadly describe the expansion that the research scope in writing on international legal history and its theory has experienced since the turn of the twenty-first century. However, the expression may come across as a misnomer. This is so, first, because the academic phenomenon this byword purports to capture is not exclusive to international law as a disciplinary field alone but also encompasses several other disciplines, namely legal history, the history of international relations, the history of political thought, and history, which as a discipline has for some time now been engaged in its own ‘international turn’. Therefore to reflect the growingly interdisciplinary cultivation of the history of international law, which partly accounts for some of its contemporary features, including a new set of historiographical and methodological debates and interdisciplinary dialogues, the recent expansion and diversification experienced by this research field may be more adequately described as a ‘turn to the history of international law’.

Feminist or gender-centred approaches to the history of international law can be very broadly identified by their object of historical investigation, namely the study of the impact of international law on the status and treatment of women across different historical periods and regions, the role played by women, both as individuals and as a group, as agents of international legal change, and their intellectual contribution to international legal scholarship over time. They can also be broadly identified by their common animus historiandi. The chief purpose driving a historical investigation into women’s histories in international law is that of redressing the ‘invisibility of women’ in the history of international law. This finds its justification in a primary need to bridge gaps that exist in the historical record of international law so as to make international legal history as complete, inclusive, and accurate as possible. It is also premised on the acknowledgement that, as the historian Gerda Lerner noted, ‘the fact that women were denied knowledge of the existence of women’s history decisively and negatively affected their intellectual development as a group’. The animus historiandi of feminist or gender-centred approaches to the history of international law may also involve contributing to the theoretical exemplification of the purported ‘patriarchal basis’ and ‘male-gendered nature of international law and its doctrines’ in a historical perspective, in particular when the analysis is informed by critical feminist perspectives. This is part of a broader use, according to Christine Chinkin, of ‘feminist theory as a basis for critical analysis, that is to show how the structures, processes, and methodologies of international law marginalize women by failing to take account of their lives or experiences’ today, as they have also largely done throughout history.