Before Pearl Harbor the Japanese had already begun imperial expansion in Manchuria, (1931) Inner Mongolia, (1936) Jehol, (1933) China, (1937) and in other territories and islands during World War 1. The Empire of Japan entered World War II on 27th, September, 1940 by signing the Tripartite Pact with Germany and Italy, and the Japanese invasion of French Indochina, though it wasn't until the attack on Pearl Harbor on 7 December 1941 that the U.S. entered the conflict. Over the course of seven hours there were coordinated Japanese attacks on the U.S. -held Philippines, Guam and Wake Island, the Dutch Empire in the Dutch East Indies, Thailand and on the British Empire in Borneo, Malaya and Hong Kong. The strategic goals of the offensive were to cripple the U.S. Pacific fleet, capture oil fields in the Dutch East Indies, and maintain their sphere of influence of China, East Asia, and also Korea. It was also to expand the outer reaches of the Japanese Empire to create a formidable defensive perimeter around newly acquired territory.