The United Kingdom and the League of Nations played central roles in the diplomatic history of the interwar period 1920-1939 and the search for peace. British activists and political leaders help plan and found the League of Nations, provided much of the staff leadership, and Britain (alongside France) played a central role in most of the critical issues facing the League. The League of Nations Union was an important private organization that promoted the League in Britain. By 1924 the League was broadly popular and was featured in election campaigns. The Liberals were most supportive; the Conservatives least so. From 1931 onward, major aggressions by Japan, Italy, Spain and Germany effectively ruined the League in British eyes.