The two world wars were the largest international conflicts of human history and had a decisive impact on all the countries that took part. This course examines their often disputed origins, their military history including changing weapons and strategy, and the social and economic transformations they fostered. We assess the successive postwar settlements, including the transition to the cold war and the end of the European colonial empires. We also take up the mobilization of ideologies—fascist, communist, and democratic—issues of genocide and postwar war-crime trials, and the legacies for film, art, and memorials. The recorded lectures are from the Harvard Faculty of Arts and Sciences course Societies of the World 42.