In the 1930s, the Great Depression wrecked Japan's economy and gave radical elements within the Japanese military the chance to realize their ambitions of conquering all of Asia. In 1931, the Kwantung Army (a Japanese military force stationed in Manchuria) staged the Mukden Incident, which sparked the Invasion of Manchuria and its transformation into the Japanese puppet state of Manchukuo. Six years later, the Marco Polo Bridge Incident outside Peking sparked the Second Sino-Japanese War (1937–1945). Japanese troops streamed into China, conquering Peking, Shanghai, and the national capital of Nanking; the last conquest was followed by the Nanking Massacre. In 1940, Japan entered into an alliance with Nazi Germany and Fascist Italy, two similarly militaristic states in Europe, and advanced out of China and into Southeast Asia. This brought about the intervention of the United States, which embargoed all petroleum to Japan. The embargo eventually precipitated the Attack on Pearl Harbor and the entry of the U.S. into World War II.