Although few could define it, “civilian morale” became one of the twentieth century’s most lethal concepts. In its name, millions of civilians were bombed and starved, as belligerents sought to break enemy morale through air raids and food blockades. How did it become normal to wage war by attacking cities and civilian morale? From the First World War through the Second, ideas and practices surrounding morale and the “home fronts” circulated rapidly in a transnational process. During 1914–18, states claimed to have discovered “civilian morale”: British and German blockaders explicitly targeted it, while governments in Germany, Austria-Hungary, Russia, and France compiled national “moral reports.” Interwar strategists such as Giulio Douhet and Hugh Trenchard argued that aerial bombardment would decisively shatter civilian morale. These ideas culminated in the area bombing of German and Italian cities during the Second World War and also shaped the Asia-Pacific theatre. Japanese air forces bombed Chinese cities in 1937–39 with morale as a central target, while U.S. strategists later endorsed firebombing and food blockades—including “Operation STARVATION” in 1945—as means of forcing surrender. The narrative ends in 1945 with the rise of American social psychologists who theorised morale destruction at the dawn of the Cold War.