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Kant in the Age of Thucydides

  • Published
  • By Dr. Jared Morgan McKinney

For the past generation, one of the key ideas of International Relations (IR) theory has been that of “Kantian peace.” Following its introduction by Michael Doyle in 1983, it became an empirical research paradigm intended to explain the relative peace of the modern era as well as the necessary conditions for unlocking peace in the future. The 2000s were the golden era of the “Kantian peace” research agenda, with scholarly papers published on the subject racking up hundreds of citations. According to researchers in the paradigm, Immanuel Kant’s vision of peace rested on a tripod of representative democracies, economic interdependence, and international law/organizations.1 States that could claim these three inputs were “fundamentally different.”2 Whether such peacefulness extended to others lacking the “Kantian tripod” was debated, but eventually scholars came to restrict the peace to within the tripod community. The way to extend the peace was to extend the tripod. Such a desire influenced the decision to invade—and remake—Iraq in 2003.3

Since 2015, as the failure of the Iraq War became indisputable and as America’s attention turned to other matters, another idea became prominent in public discourse: the “Thucydides Trap.” The graph below, charting instances of these phrases in published books, shows the trends.4

Figure 1: Thucydides Trap

The “Thucydides trap,” like the Kantian peace, invokes the name and pedigree of a great historical thinker to articulate the concerns of the moment. At this particular juncture, the idea is that a power transition between the United States and China makes war “inevitable.” Unfortunately, as I have argued elsewhere, today’s Thucydides trap relies on a caricatured and simplistic reading of the Greek historian.5 In a similar manner, careful readers of the German philosopher Immanuel Kant also know that his original ideas—composed more than two centuries ago—have also been misinterpreted and employed as a prestige tool to justify contemporary positions.6 Although Thucydides is the thinker of the moment, in this short essay I shall return to Kant for his theory of peace—properly assessed—should inform how policymakers think about avoiding war in an era of increasing (Thucydidean) Great Power Competition.    

Kant’s ideas on peace, famously articulated in his 1795 essay “Perpetual Peace,” should first be set in the context of his wider interpretation of social reality found in his earlier (1784) essay “Idea for a Universal History.”7 Here, he argued in a series of propositions that humankind was developing through the accumulated learning of the species over time, that this development was driven by a process of “unsocial sociability” wherein the competitive desire for “honour, power, or property” provoked the awakening of dormant capabilities, but that this antagonism needed to be balanced with order lest discord cause a “hell of evils to overtake us.” Order was to be found in a “master,” which for domestic society would preferably be a “just civil constitution.” Likewise, international society required a “federation of peoples” governed by law. The creation of these domestic and international societies, Kant believed, reflected the “hidden plan of nature.” His essay bears the title it does because he proposes that an empirical history be developed along these lines.

“Perpetual Peace,” the essay that followed a decade later, outlined how Kant’s envisioned “federation of peoples” was to be secured. The essay, presented in the form of a treaty, contained “preliminary articles” and then “definitive articles.” Perpetual peace was to be approached “by an infinite process of gradual approximation.”8 Modern IR scholars, who have appealed to Kant in order to justify democratic peace, collective defense, and international law, ignore his “preliminary articles.” They also revise and simplify his “definitive articles.”

Kant’s “preliminary articles” included abolishing standing armies (article 3), forbidding the contraction of debt in war (article 4), pledging oneself to non-intervention in the governance or civil wars of others (article 5), and electing not to pursue “dishonourable stratagems” during war—which were generally anything that would make the negotiation of peace at a later point impossible—and specifically were said to include assassinations, breaches of agreements, and the recruitment of spies. Notably, none of these articles have been adopted by any of the world’s major states today. The uncomfortableness of their content suggests humankind may not be as far along on the road to perpetual peace as many would prefer to assume.

For this reason, perhaps, modern IR scholars have begun with Kant’s “definitive articles.” But their revisions are telling. Whereas “democracy” today is considered the key determining quality of a polity’s regime type, most modern states would not fit Kant’s actual requirement, which mandated that a legislative decision for war—which requires the consent of the people—be separated from the executive’s prosecution of such a war. Although the US meets this standard in theory, the executive branch in practice has monopolized war decisions since the Korean War. By Kant’s actual standard, the modern US—and many others, including the UK—do not have a republican form of government. Kant’s second “definitive article,” a federation of free states, presumed the adoption of the first article. His third “definitive article” was not in fact free trade, but a cosmopolitan norm of hospitality.

In the League of Nations and the United Nations, something like Kant’s “general agreement” to vindicate rights by legal means rather than by force was indeed established. In combination with the apparent growing strength of the “international community”—seen, for instance, in collective sanctions—and the spread of universal values and sentiments, many today have come to feel that the community of nations “has developed to the point where a violation of rights in one part of the world is felt everywhere” which was Kant’s postulated eventual outcome during the order of perpetual peace. Kant believed this end state would occur through “continuous progress” without “any more total reversals.”9 While this belief cannot be justified given the horrors of the Second World War as well as the genocides of the twentieth century, many thinkers today assume that the world has become (or is becoming) essentially peaceful.10

The question might be put simply: is the international system in the state of nature, or has it acquired a “master” and entered into a state of perpetual peace? The question can be answered empirically: even if there are not active hostilities ongoing, there is now “a constant threat of their breaking out,”11 which is Kant’s definition of the state of nature—the state opposed to that of perpetual peace. This is what all the talk about Thucydides and Great Power Competition is about.

For all the cosmopolitan ideals of international society, peace has not, or to be more precise, is not currently formally instituted between many of the world’s states, including the Great Powers, the US, Russia, China, India, and Japan. This recognition is important because a political agenda that seeks to implement the definitive articles of peace (a republican form of government, federal institutions, and cosmopolitan rights by Kant’s account; democratic government, a democratic league, and international trade, by the modern account) while neglecting the preliminary articles, orients states backward towards the state of nature by making war more likely—and all in the name of peace and right! Such confusion of humankind’s condition has been seen in Iraq, Libya, and Syria where the tactic of revolution was attempted to secure perpetual peace. These attempts were failures for reasons Kant himself understood; progress and peace were to be achieved through the victory of reason and cosmopolitan socialization (which included gentle commerce), not that of force, for the foundation of the latter was shaky.12

To formally institute peace (in a preliminary rather than definitive sense) with a power such as China or Russia, both of which reflect a ‘regressive’ political tradition wherein the government “reflects the will of the people only in so far as the ruler treats the will of the people as his own private will,” would be to compromise with the ultimate good, right, and justice of definitive perpetual peace (which Kant envisioned for republican states).13 Such a formal preliminary institution of peace would aim to nullify “all existing reasons for future war.”14 Territorial disputes (whether over Crimea, the Himalayas, Taiwan, or islands in the South and East China Seas) are the most prominent form of such disagreements. The preliminary institution of peace would also require the regulation of “the essentially healthy hostility which prevails among states and is produced by their freedom.”15 Arms control agreements, and the tempering of ideological disagreements, are examples of such regulation.  The necessity for such compromise derives not from moral bankruptcy or weakness, but from the frank recognition that demanding Heaven Now will instead cause “a hell of evils to overtake us,” destroying the good and progress humankind has today achieved.16 In the long one, the goodness and justice of perpetual peace may or may not be possible (and inevitable, as Kant believed), but without the institution of a preliminary peace, we shall never know.

In summary, Kant is surely correct that it is time to move beyond the “vain and violent schemes of expansion” that generate debt and the potential for “barbaric devastation.” But leaders interested in making such a move should begin with Kant’s preliminary articles, which are in themselves challenging enough. And when they look to his definitive articles, they should read what he actually wrote rather than the potted summaries so common in popular IR renditions today. Two centuries of experience have suggested that achieving a republican and cosmopolitan “master” in a league of nations is not realistic in the short term. But seeking to get away from the state of nature through preliminary articles of peace, including the formal resolution of the issues most likely to generate wars, makes eminent sense given the likely costs of conflict in an age of globalized supply chains, technological dependence, and nuclear weapons.

In an era of Thucydidean rivalry, Kant’s second “supplemental article of perpetual peace” should be evoked: the duty of states “armed for war” to consult the “maxims of the philosophers on the conditions under which public peace is possible.”17 The imperative of today—and for however long Great Power rivalry persists—is to check the excesses of international competition while still reaping the benefits of “healthy hostility” in which different versions of human freedom compete. In the words of the Shanghai Communiqué, a document that needs to be rediscovered as relations between the US and China grow more tense, “Countries should treat each other with mutual respect and be willing to compete peacefully, letting performance be the ultimate judge.”18 This agreement was negotiated by Henry Kissinger and Richard Nixon, the uber “Realists” of America’s tradition. But Immanuel Kant, the uber “Liberal” of the Enlightenment, would have recognized in this equation a model equilibrium between concord and discord that secured peace while maintaining freedom. Policymakers and public intellectuals would do well to revisit this tradition.

Dr. Jared Morgan McKinney
Dr. Jared Morgan McKinney is an Assistant Professor at the Global College of PME, Air University, and Reviews Editor at the Journal of Indo-Pacific Affairs. Opinions, conclusions, and recommendations expressed or implied within are solely those of the author and do not necessarily represent the views of the Air University, the United States Air Force, the Department of Defense, or any other US government agency.


1 Bruce Russett and John Oneal, Triangulating Peace: Democracy, Interdependence, and International Organizations (New York: W. W. Norton & Company, 2000).
2 Michael W. Doyle, “Kant, Liberal Legacies, and Foreign Affairs,” Philosophy & Public Affairs 12, no. 3 (Summer 1983): 235.
3  Patrick Porter, Blunder: Britain’s War in Iraq, First edition (Oxford, United Kingdom: Oxford University Press, 2018), chap. 2.
4 “Google Books Ngram Viewer,” Google, 13 May 2021,
5 Jared Morgan McKinney, “Putting Thucydides Back into the ‘Thucydides Trap,’” China-US Focus, October 8, 2015,
6 Luigi Caranti, “Kantian Peace and Liberal Peace: Three Concerns: Kantian Peace & Liberal Peace,” Journal of Political Philosophy 24, no. 4 (December 2016): 446–69,; Sid Simpson, “Making Liberal Use of Kant? Democratic Peace Theory and Perpetual Peace,” International Relations 33, no. 1 (March 2019): 109–28,
7 Immanuel Kant, Kant: Political Writings, ed. Hans Siegbert Reiss, 2nd ed. (New York: Cambridge University Press, 1991).
8 Kant, “Perpetual Peace,” in Kant: Political Writings, 130.
9 Kant, “The Contest of the Faculties,” in Kant: Political Writings, 184, 189.
10 Mark Levene, “Why Is the Twentieth Century the Century of Genocide?,” Journal of World History 11, no. 2 (2000): 305–36,; Steven Pinker, The Better Angels of Our Nature: Why Violence Has Declined (New York: Penguin Books, 2012); Oona Anne Hathaway and Scott Shapiro, The Internationalists: How a Radical Plan to Outlaw War Remade the World (New York: Simon & Schuster, 2017).
11 Kant, “Perpetual Peace,” in Kant: Political Writings, 98.
12 “Postscript” in Kant: Political Writings, 252.
13 Kant, “Perpetual Peace,” in Kant: Political Writings, 101.
14 Kant, “Perpetual Peace,” in Kant: Political Writings, 93.
15 Kant, “Idea for a Universal History,” in Kant: Political Writings, 49.
16 Kant, “Idea for a Universal History,” in Kant: Political Writings, 48.
17 Kant, “Perpetual Peace,” in Kant: Political Writings, 115.
18 “Joint Statement Following Discussions with Leaders of the People’s Republic of China” Foreign Relations of the United States, 1969–1976, Volume XVII, China, 1969–1972 - Office of the Historian, 27 February 1972,

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