In the field of critical international law, few figures who have attempted to transform the discipline’s imaginative horizons have proven as influential as Martti Koskenniemi. Yet, while either his structuralist delineation of international legal argument in From Apology to Utopia or the key role he played in inaugurating international law’s “turn to history” in The Gentle Civilizer of Nations would have warranted an understandable “ride off into the sunset”, Koskenniemi shows no signs of slowing down. Rather, his latest endeavor concerns the historical relationship between property and sovereignty.  For Koskenniemi, the need for this intervention is evident from the fact that the recent proliferation in critical international legal history has typically consigned itself to “public” issues of war, peace, and diplomacy. This has led to widespread neglect of the formative influence of property, commerce, and finance, which are generally viewed as matters of “private international law”. In advancing the claim that comprehensive critical histories of international law must grapple with the “private” no less than the “public”, Koskenniemi states that:
“if power and authority are the ultimate subjects of these histories, then their scope must be expanded to also capture the migration that has separated the two types of law–sovereignty and property–from each other as well as how, despite their different trajectories, the two can only be well understood in their relationship with each other. They are the yin and yang of global power.” 
While this renewed approach to international legal historicisation presents exciting prospects, especially for Marxists, a pitfall properly evaded at this early stage is the potential contradiction between this sovereignty-property project and Koskenniemi’s earlier project of disavowing the influence of the field of international relations in international legal theory. This project commenced with Koskenniemi’s affirmation of a “culture of formalism” as a necessary tactic in the face of American power, the post-Second World War expansion and consolidation of which dethroned international law from its status as the supreme “explainer” of “how the world actually works”. This occurred through realist theories of international relations, which divorced morality and legality from “the international”, this being understood as a purely “political” realm of struggle and survival. For Koskenniemi, this engendered a “culture of anti-formalism” tantamount to a crass apology for US global dominance, which international lawyers had a strong political stake in opposing with a “culture of formalism”. 
However, the threat to international law from international relations was in no way confined to realism. A potentially even more pernicious threat emerged with the cosmopolitan triumphalism of the post-Cold War era, when many liberal institutionalists attempted to intrumentalise international law by reducing it to simple metrics of “compliance”. It is against the background of these later developments that Koskenniemi has discussed “counterdisciplinarity”, underscoring the importance of law’s teleological orientation toward an imagined better world and insisting that this orientation stands in opposition to attempts on the part of international relations scholars to evaluate “scientifically” the here and now. 
Yet what about dissident perspectives within the discipline of international relations, those that are just as critical of realism, liberal institutionalism, and American hegemony as anything that may have emerged through the legal “culture of formalism”? Further, what if such perspectives engaged sophisticatedly with the same historically delineated sovereignty-property relationship that Koskenniemi deems central to the work of international lawyers? These are not merely rhetorical questions. Analysis of how the entrenchment of an ideological distinction between “public” and “private” grounded in class conflict and social property relations gave rise to the conceptual architecture of the international order has informed an ongoing line of inquiry in Marxist historical sociology, with Justin Rosenberg’s The Empire of Civil Society and Benno Teschke’s The Myth of 1648 being two particularly foundational contributions. Moreover, Koskenniemi has acknowledged the existence of such approaches and has recently made it clear that they have yet to exert significant influence over international law’s ongoing “turn to history”. 
When considering just how deep the resonance between these approaches and Koskenniemi’s sovereignty-property project really is, what must be considered are Koskenniemi’s statements on methodology in the writing of international legal history. In his “A History of International Law Histories”, Koskenniemi notes that efforts to move beyond strictly doctrinal developments and produce histories of international law’s actual impact have suffered from inattention to the “historical sociology of international relations”.  As such, they present explanations as self-revealed truths in a way that is problematic and methodologically unjustified.  Yet given his earlier claim that international relations scholars subscribe to a view of the world with which international lawyers cannot engage without degrading their field’s essential purpose, what are we to make of explanations of the material development of international law that have emerged as responses to debates within the field of international relations? From a Marxist perspective, how could maintaining this ideological aversion toward another field, in spite of the opportunities for valuable substantive and methodological cross-fertilization, be anything other than disciplinary fetishisation?
This leaves open the question of how to account for the unique function of law and legal reasoning within the broader field of Marxist approaches to international historical sociology. After all, maintaining this domain for international law as a particularly unique way of viewing the world is precisely what is sought by those who have recourse to arguments about “counterdisciplinarity”. Is it possible to account for this uniqueness without the idealized abstractions that accompany the fetishisation of disciplinary boundaries? One theoretical orientation that confronts such questions directly is what Anne Orford dubs “juridical thinking”–a phenomenon in which law is broached genealogically.  According to this orientation, international lawyers connect otherwise unrelated historical events with overarching systems of meaning, and this explains their deviation from context-centric “Cambridge School”-type approaches. 
By engaging explicitly with “juridical thinking” as a distinct form of historicisation that is compatible with parallel historical explanations, the theorist is forced to confront the issue of how multiple registers of historicisation (and their political consequences) bear upon larger synthetic efforts. Awareness of this delivers a powerful blow to any attempt to retreat into the ahistorical. Moreover, this must be considered in conjunction with the influence that Marxist approaches have had within the larger field of international relations, including the integration of insights from economic history, global history, and historical sociology as a means of recontextualizing debates generated through an originally “scientific” method of explanation.  Accounting for the particular functions of legal argumentation and “juridical thinking” within this new, materially grounded mode of explanation is a project that is only just beginning. Through his new project of sovereignty-property, Koskenniemi has laid the foundations for an entirely new generation of the type of international law-international relations interdisciplinarity that, ironically enough, he himself has long made a point of disavowing.
 See, e.g., Martti Koskenniemi, “Sovereignty, Property, and Empire: Early Modern English Contexts”, 18 (2017) Theoretical Inquires in Law 355.
 Martti Koskenniemi, “Expanding Histories of International Law”, 56 (2016) American Journal of Legal History 104, at 112.
 Martti Koskenniemi, The Gentle Civilizer of Nations: The Rise and Fall of International Law, 1870–1960 (Cambridge: Cambridge University Press, 2001), 494–496.
 Martti Koskenniemi, “Law, Teleology and International Relations: An Essay in Counterdisciplinarity”, 26 (2012) International Relations 3.
 Koskenniemi, “Expanding Histories”, 107.
 Martti Koskenniemi, “A History of International Law Histories”, in Anne Peters and Bardo Fassbender (eds), The Oxford Handbook of the History of International Law (Oxford: Oxford University Press, 2012) 943, at 961 (emphasis mine).
 Ibid., 961–963.
 Anne Orford, “On International Legal Method”, 1 (2013) London Review of International Law 166.
 Ibid., 175–176.
 See Barry Buzan and George Lawson, The Global Transformation: History, Modernity and the Making of International Relations (Cambridge: Cambridge University Press, 2015).
Eric Loefflad is a doctoral candidate in law at the University of Kent.