In their spirited contribution “Might Unmakes Right” in the July/August issue of Foreign Affairs, Oona A. Hathaway and Scott J. Shapiro warn of the looming erosion of one of the central norms of international law: the prohibition of the use of force. They cite breaches such as the illegal U.S. invasion of Iraq in 2003, China’s expansion in the South China Sea, and Russia’s full-scale invasion of Ukraine in 2022. Above all, however, they argue, it is Donald Trump who “is shredding what is left of the norm against using force.”
One can only agree with Hathaway and Shapiro that international law is under mounting pressure. “If left unchecked,” they write, “the erosion of the prohibition on the use of force will return geopolitics to a raw contest of military power.” Much is at stake – and the time to defend the law is now.
However – and this is the reason for my brief reply – what is unconvincing in Hathaway and Shapiro’s argument is their teleological narrowing of the historiography of the modern ius contra bellum, on which their case rests. In this post, drawing on my new book A Century of Anarchy?, I contend that the roots of the modern prohibition of war reach further back than they claim – and that the stark old-versus-new order dichotomy they draw is, historically, untenable.
Old Order, New Order: The Lure of Black-and-White Thinking
Building on their 2017 book The Internationalists, Hathaway and Shapiro argue that the Kellogg-Briand-Pact of 27August 1928 ushered in a new world order: for the first time, war was declared illegal under international law. Prior to that, they write:
‘[w]ar was considered legal, the primary way to enforce national rights and resolve disputes between states. (…) For centuries before World War I, war was a legally recognized means by which states resolved disputes. The outbreak of war did not constitute a breakdown of the international order – it was the order.”
Black and white, then: an old world order before 1928 in which war was legal, and a new one thereafter in which, through a sudden big bang, war was banned and the world made more peaceful. It is entirely understandable that the current threats posed by Putin, Xi, Trump, and others seem especially alarming within such a nostalgic tale of progress in the history of the prohibition of the use of force.
The core problem with Hathaway and Shapiro’s account, however, is that it does not withstand historical scrutiny – or is, at the very least, highly reductive. The notion of a “free right to go to war” (liberum ius ad bellum), which continues to feature among the founding myths in the History of International Law and International Relations, never in fact existed. As I have argued in my book, war was, even before 1928, widely regarded as a problem in international relations.
The idea that war was always legal prior to that, as Hathaway and Shapiro contend, is ultimately a reimagining of history – one that can be traced back to military-affiliated, Clausewitzian lawyers in the late nineteenth century who wrote in opposition to a liberal mainstream in Europe. In the interwar period, this myth of a free right to go to war was universalized, promoted by realists such as Nazi lawyer Carl Schmitt. Surprisingly, however, liberals also sought to cast the legal advances of their own era in a brighter light. A dark nineteenth century, in which states could always resort to war, conveniently served the narrative of a radical transformation from an old to a new world order – a narrative that Hathaway and Shapiro continue to sustain.
A Genealogy of Modern Ius Contra Bellum Beyond Black and White
But this old black-and-white story of the modern ius contra bellum is untenable. The nineteenth century was neither an age of international anarchy nor the photographic negative of the modern order – it was, in fact, the era of its birth.
As Hathaway and Shapiro rightly argue, the Kellogg-Briand Pact marked the first time in history that war was generally prohibited by treaty. However, the emphasis on treaty law here is crucial. Even prior to the Kellogg-Briand Pact, war required justification. When states went to war, they justified it. Hathaway and Shapiro acknowledge this need for justification and, drawing on the pioneering 2012 work of German early modern historian Anuschka Tischer, they have collected numerous war manifestos.
Hathaway and Shapiro are, of course, right to note that these justifications were always also propaganda. Their conclusion, however – “because no supreme authority existed to judge the legality of wars, the international system effectively presumed that every conquest was just. Might made right.” – does not hold up historically. The more than 400 war declarations they analyzed from 1492 to 1945 do not show that law and power were identical in the old order.
On the contrary: the historically consistent need to justify war suggests that violence in international politics was regarded as problematic even before 1928. Hathaway and Shapiro underestimate what Anuschka Tischer has demonstrated with greater nuance: Tischer has conducted a systematic study of more than 300 early modern war manifestos within various courtly communication communities and found that they could indeed exert a restrictive effect on violence. A reason had to persuade. If it did not, even powerful actors would find themselves struggling to explain their actions. Might did not make right.
In discourses on the use of force, what was considered acceptable in international or inter-polity relations has always been discussed, confirmed, contested, or further developed. There is a dialectical relationship between the justification of war and the shaping of international order. This story is not only one of continuity but also of change: Hathaway and Shapiro aptly observe that in the early modern period, the grounds for war were relatively broad and vague and that over time, these justifications were increasingly narrowed to self-defense. But the key transformative era in this process – Europe’s “long nineteenth century” (1789–1914) – is neither addressed in their book nor in their Foreign Affairs article. Nor do they mention perhaps the most influential modern thinker behind the legal prohibition of war: the Prussian philosopher Immanuel Kant.
But the European nineteenth century is essential to understanding the genesis of the modern international order governing the use of force. The “radical plan” to limit or even prohibit war did not first arise in the early twentieth century, as Hathaway and Shapiro suggest. It had already been outlined in the increasingly professionalized legal debates of the nineteenth century. Already in the first half of the nineteenth century, European and US lawyers such as Klüber, Heffter, Wheaton, Zachariä, H. B. Oppenheim, Kaltenborn-Stachau, and, somewhat later, Mohl rejected the notion of war as a legitimate instrument of politics. In the second half of the century, figures such as Bluntschli and, above all, Walther Schücking further developed a ius contra bellum inspired by Kant. Yet Hathaway and Shapiro make no mention of this. In their account, pacifist legal discourse seems to appear ex nihilo in the United States around the turn of the century.
An equally pivotal moment in the development of the modern international order governing the use of force – alongside 1928 – was 1814/15. In the wake of the traumatic Napoleonic Wars, the Congress of Vienna established the European Concert of Great Powers, a ‘nineteenth-century Security Council’ that for the first time assessed the legitimacy of international violence in congresses and conferences. Through diplomacy and mediation – as well as ‘small wars’ against non-European polities, which underscore the darker, imperialistic dimensions of this peace order – it prevented system-threatening wars between European great powers, with the notable exception of the Crimean War (1853–56). As I argue, the roots of the modern prohibition of war lie in the Vienna settlement. It was not yet a treaty norm, but it was an emerging norm nonetheless – one that can be clearly identified in the justificatory practices of the nineteenth century.
In Hathaway and Shapiro’s account, the nineteenth century hardly features as a distinct era at all. It is simply folded into the “old order” from circa 1600 to 1928. Only by omitting it can they sustain their stark dichotomy between old and new orders. Historically, however, that dichotomy is flawed. The modern discourse of ius contra bellum emerged in the nineteenth century.
(Which) Lessons from the Past?
This is not merely a question of historiography – it directly shapes how we think about the current “crisis” of international law. If the norms against the use of force have a much longer history than 1928, we must ask ourselves what lessons we can learn from this longue durée for the shaping of these norm today. Does it suggest hope – or pessimism?
Let me be clear: I share Hathaway and Shapiro’s call to defend international law. On this point, I am fully aligned with them. I also agree with their warning that “today’s leaders must design institutions, alliances, and strategies to secure peace rather than sit and watch as Trump rewinds the clock.” This is exactly right. What the world needs now is not fatalism or disregard for international law, but a resolute commitment to its normative power.
That said, I argue – contra Hathaway and Shapiro – that the history of modern ius contra bellum is much longer than they suggest. This, however, does not weaken their case for defending international law. On the contrary, it strengthens it by offering a broader repertoire of historical examples illustrating the importance of norms in international relations. For the history of war is also a history of its justification and critique. This can, of course, be read pessimistically: although efforts to overcome international violence have a much longer history than often assumed, war remains part of our reality – despite ongoing debates about its possible decline – whether openly declared or framed as self-defense in letters to the UN Security Council. But what matters is that even the most power-hungry politicians, including Adolf Hitler on 1 September 1939, sought to justify their wars of aggression, thereby performatively acknowledging the norms themselves.
Here is where a new alliance of middle powers can step in, defending the law against Trump, Putin, Xi, and others. The long history of war justifications shows that pressure can – and must – be exerted against the disregard of law in war discourses, including persistent double standards. The history of norms against the use of force is longer and less teleological than Hathaway and Shapiro believe – and it is precisely in this longue durée that a glimmer of hope can be found.