Military planners during the inter-war period laboured under the shadow of the Great War. In addition to untold human suffering, four long years of armed conflict wrought profound changes within and among states. What began in 1914 as a European war grew into a global conflict, involving belligerents from five continents, even if the bulk of the fighting occurred on European battlefields. The globalization of the war reflected Europe’s loss of political and economic pre-eminence as hitherto rising countries, most notably the United States, emerged as undisputed great powers capable of decisively influencing world events. Within Europe and on its borderlands, the defeat of the central powers, together with the disintegration of four empires (the Russian, Austro-Hungarian, German, and Ottoman) and the creation of ‘successor’ states, remade geographical and political maps. The military landscape also changed with the growing use of weapons, such as the tank and the airplane, which promised to re-introduce mobility to the battlefield and to dissolve existing boundaries between civilians and combatants. Within belligerent countries, the Great War saw a remarkable increase in state power and capabilities as governments, compelled by the insatiable demands of modern industrial warfare, oversaw a massive mobilization of national resources. This unprecedented effort contributed to a reconfiguration of political, economic and social power within countries, with sometimes far-reaching consequences for international stability.