World War II was fought for many reasons, stretching back to the end of World War I. But the main cause of World War II was the rise of dictatorships in the 1930s. There were dictators in many countries, but the most powerful and militarily aggressive were the Nazi dictatorship of Adolf Hitler in Germany, the Fascists under Benito Mussolini in Italy, and the militaristic state that arose in Japan, eventually under the leadership of Hideki Tojo. Joseph Stalin in the Soviet Union also oversaw a murderous Communist dictatorship, but his immediate territorial ambitions were rather limited compared to those of his peers. Indeed, it was the expansionist nature of these dictatorships that sparked the crisis that led to the outbreak of war. Japanese expansion in the Pacific and China brought it into conflict with the United States in 1941, Hitler's ambitions to conquer Europe led to war with England and eventually the Soviet Union, and Mussolini attempted to expand into North Africa. These dictatorships, through their actions, sparked World War II, which, from an Allied perspective, was largely about rolling back their territorial gains and destroying their regimes.