This post is an advance version of a review essay that will appear in Humanity volume 10. It will be posted in five parts: one each day this week. This is part 4.
Hathaway and Shapiro claim that “the outlawry of war in 1928—and the broader legal transformation that it unleashed—made it safer to trade” (344). By introducing a safeguard against conquest, Kellogg-Briand released the energies of free trade and colonial nationalism, resulting in a globalized world economy and a quadrupling of the number of independent sovereign states around the world after 1945. The Internationalists claims that before the Paris Peace Pact, the gains that accrued to imperialism and conquest led to states becoming “bigger and less numerous” and that they traded little because “they feared their trading partners” (341-42). It is an elegant argument backed up by abundant data.
It is undeniable that by banning war, Kellogg-Briand made the world safer for small states in the long run. The devil is in the details, however. There was already a secular increase in the number of independent states and a sustained rise in global trade in the century before 1928. The Correlates of War data used by Hathaway and Shapiro show that whereas only 23 internationally recognized sovereign states existed in 1816, some 45 were in existence by 1914 (Figure 3, 338). It is also a well-established fact that world trade and investment grew enormously between the mid-nineteenth century and World War I. In proportional terms the level of foreign investment in developing countries at the end of the Edwardian era was not seen again until the late 20th century. In 1917, the total amount of world trade reached one third of the value of global output, the highest level that would be recorded until 1972. In other words, economic history does not suggest that the legality of war prior to Kellogg-Briand was a major obstacle to international trade.
The expansion of global trade unleashed in the 1850s was initially a purely commercial process. Once the boom ended in the 1873 depression, territorial conquest gained in appeal. The acquisition of land by conquest by imperial powers reached 6 million square kilometers in the 1870s, nearly 9 million square kilometers in the 1880s, and over 7 million square kilometers in the 1890s. This was the age of European and American high imperialism. But thereafter conquest fell precipitously: by the 1920s, the size of territorial conquests had fallen to the level of the 1820s; less than 1 million square kilometers per year. Of course, there is only so much land on Earth that can be conquered, so territorial imperialism inevitably faced diminishing returns. Yet as long as conquest was legal, land could change hands indefinitely. That territorial conquest did not remain high but instead started to stabilize after the 1890s, and thereafter showed a declining number of conquered square kilometers per decade, is clear from Hathaway and Shapiro’s data (Figure 1, 317).
The way in which Hathaway and Shapiro have construed the data from the Correlates of War project in support of their argument is open to dispute. In a bar chart of territorial conquest in different period (Figure 2, 320), they show that the number of internationally accepted territorial conquests that occurred was very high in the period from 1816 to 1928, declined from 1929 to 1948, and fell to almost nil from 1948 to 2014. The long-term trend is undeniable. Yet by extending the first period up until 1928, Hathaway and Shapiro miss that the immediately preceding years since 1921 were already a nearly conquest-less period.
The record of conflicts and territorial changes in that database shows that territorial conquest virtually ceased to exist already after March 1921, when the Polish-Soviet War was concluded and the territorial division of Eastern Europe stabilized. Seventeen transfers and four exchanges of territory took place worldwide between March 1921 and April 1928. Most territorial transfers were concluded by bilateral treaties to solve border disputes; some were the outcome of mediation or mandates by the League of Nations; others resulted from arbitrations by third parties. Just two cases involved force: in May 1922 the United States unilaterally annexed Kingman Reef, a shoal between Hawai’i and American Samoa, as an unincorporated territory; and in January 1923 Lithuania occupied the French-occupied Klaipėda region on the Baltic after the local ethnic Lithuanian majority revolted and petitioned the League to be granted the right to unite with their compatriots, a request formally approved by Geneva in 1924. Even on an expansive definition of war (fourteen people were killed on all sides in the five-day Klaipėda Revolt), then, in the seven years before Kellogg-Briand the total territory claimed by force all over the world amounted to some 2,850 square kilometers (1,100 square miles) of territory—a total the size of the U.S. state of Rhode Island. It is hardly what one would expect in an international order where conquest and aggressive war were rife. The League machinery brought into existence in the aftermath of the Great War therefore has at least as good a claim as Kellogg-Briand to being the gravedigger of recognized wars of conquest.
What explains the fall in the size of territorial conquest in the period between 1890 and 1920, as well as the absence of territorial changes through war after 1920/21? A major transformation of the global economy and the character of statehood was well underway by the time Kellogg and Briand signed their treaty. Colonial conquest was on the decrease and new forms of informal empire became more appealing in the 1910s and 1920s. The United States had led the way in the first two decades of the century, when it shifted to informal domination after a short experiment with open imperialism. Britain, France, South Africa, Belgium, and Japan acquired former German and Ottoman colonies and ruled them as mandatory powers under League oversight. More important was the fact that economic globalization peaked in the decade before World War I, and in many ways continued into the late 1920s. Robert Boyce has proposed that the peak of early twentieth-century globalization in institutional and financial terms may have occurred as late as 1927. If anything, it was economic globalization that enabled the Paris Pact not the other way around. When globalization collapsed in the 1930s, another round of conquest ensued. Interwar history thus suggests that the viability of conquest is linked to the fortunes of economic globalization rather than vice versa.
The explanandum of The Internationalists—why did recognized territorial conquest as the result of aggressive war nearly disappear after the 1920s?—can thus be understood historically in a way that is at once realistic about power and takes the legal prohibition on war very seriously. The great powers that signed Kellogg-Briand did so because they agreed with its rules and wanted to earnestly uphold them. Principle and interest were not at odds for the main countries involved. Their leading statesmen agreed to legally restrict the practice of war-making because the world order as it had developed by 1928 was quite beneficial to them. From the perspective of global imperial history, Kellogg-Briand appears as a very obvious move. Euro-American dominion over the rest of the world was at a peak. If there was ever a good time to put inter-imperial rivalries to the side once and for all and secure the West’s leading position in the global economy, it was now. To their credit, Hathaway and Shapiro acknowledge that “the Pact appealed to the West because it promised to secure and protect previous conquests” (159). But by not developing this insight for more than a short paragraph, they miss an opportunity to lift their history of the legal status of war to the global scale that it deserves
By 1927-1928, world-economic integration had become the major question of law and statecraft. World politics revolved more than ever before around trade and finance: the key issues of diplomacy were tariff abolition, freedom of the seas, and the still unresolved German reparations question. Having once staked its hopes for national defense on its military, Paris now looked to the Banque de France for salvation. With a competitively priced currency driving a booming economy, the Third Republic was committing itself to obtaining through economic means what it had not been able to secure through force. Germany similarly focused its efforts on leveraging American influence in Europe and on gaining access to international markets. As Susan Pedersen has shown, German officials used the League’s Permanent Mandates Commission to gain commercial entry into its rivals’ colonial economies. It was amidst broad-based perceptions of waning European global power in the face of American and Soviet competition that Briand proposed his famous plan for Western Europe’s economic unification in 1929.
From a global perspective, Hathaway and Shapiro’s “radical plan to outlaw war” thus appears as a conservative move to shore up colonial influence, consolidate European industry, and secure what territories that had been obtained through conquest by redefining the meaning of war in international law. By restricting legal war to self-defense only, new competitors were hemmed in by the international legal order. Meanwhile, granting independence to colonies and protectorates—as the British had already started doing with Egypt in 1922 and Iraq in 1932—was a price worth paying for this improvement in stability. Formal political control could be traded for informal economic influence. The autonomy offered to new states that emerged from the worldwide process of decolonization from the 1940s to the 1970s would be circumscribed by this arrangement of international law and economic power.
 Angus Maddison, The World Economy, Vol. 1: A Millenial Perspective (Development Centre of the Organisation for Economic Co-operation and Development, 2001), 127, Table 3-2b; 128, Table 3-3.
 Mariko J. Klasing and Petros Milionis, “Quantifying the Evolution of World Trade, 1870–1949,” Journal of International Economics 92, no. 1 (January 2014): 185–97.
 Another key to the boom in trade during the pre-1914 era of high imperialism and wars of conquest is the uniquely protective nature of international law at the time towards private property and foreign investment in wartime. The popularity of Cobdenite free trade ideas enshrined in the Paris Declaration meant that between 1856 and 1914, war between states in public international law was quite sharply separated from the commercial interests of individuals and firms in private international law—something that ended with the rise of economic sanctions under the New World Order. See the excellent account in Bernard Semmel, Liberalism and Naval Strategy: Ideology, Interest and Sea Power During the Pax Brittanica (London: Allen & Unwin, 1986).
 As Daniel Immerwahr has recently reminded us, the United States “briefly flirted with outright territorial conquest before turning to other, harder-to-see forms of global power,” though it never relinquished its small but important overseas territories. “The Greater United States: Territory and Empire in U.S. History,” Diplomatic History 40, no. 3 (June 2016): 375.
 Robert Boyce, The Great Interwar Crisis and the Collapse of Globalization (Basingstoke: Palgrave Macmillan, 2009), 425.
 Charles Maier, Recasting Bourgeois Europe: Stabilization in France, Germany, and Italy in the Decade After World War I (Princeton: Princeton University Press, 1975), 236.
 Susan Pedersen, The Guardians: The League of Nations and the Crisis of Empire (New York: Oxford University Press, 2015).
 The standard account is Anthony Anghie, Imperialism, Sovereignty and the Making of International Law (Cambridge: Cambridge University Press, 2004), 196–244.