 Complete the following phrase:  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 wasnt 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, 