Although there were many causes of World War II, much of the blame is traced to the failure of the Treaty of Versailles at the end of World War I. During the 1920's and 1930's, totalitarian states had established control under: Nazi leader Adolf Hitler in Germany; fascist leader Benito Mussolini in Italy; communist leader Joseph Stalin in the Soviet Union, and Emperor Hirohito in Japan. The inability of the League of Nations to deal with the aggressive acts of these nations, combined with the isolationism of the U.S., and the appeasement of Adolf Hitler eventually led to World War II. In the years following the rise of dictators in Europe, an ethnic cleansing of undesirables was carried out in Hitler's Final Solution.