In Asia, German successes encouraged Japan to call for oil supplies from the Dutch East Indies .  Many Western countries reacted to the occupation of French Indochina by banning oil trading with Japan.  Japan planned to take over European colonies in Asia to create a great defensive area in the Pacific so that it could get more resources.  But before any future invasion, it first had to destroy the American Pacific Fleet in the Pacific Ocean .  On 7 December 1941, it attacked Pearl Harbor as well as many harbors in several South East Asian countries.  This event led the United States, United Kingdom, Australia, Western Allies and China to declare war on Japan, while the Soviet Union remained neutral.  Most of the Axis nations reacted by declaring war on the United States.
Too weak to resist Japan, China appealed to the League of Nations for help. Japan withdrew from the League of Nations after being condemned for its incursion into Manchuria. The two nations then fought several battles, in Shanghai , Rehe and Hebei , until the Tanggu Truce was signed in 1933. Thereafter, Chinese volunteer forces continued the resistance to Japanese aggression in Manchuria , and Chahar and Suiyuan .  After the 1936 Xi'an Incident , the Kuomintang and communist forces agreed on a ceasefire to present a united front to oppose Japan.