 The tipping point came just after the Nazi invasion of the Soviet Union in late June 1941.With the Soviets tied down, the high command concluded that a "strike south" would solve Japan's problems with the United States, most notably the increasing American concerns about Japan's moves in China, and the possibility of a crippling oil embargo on Japan.To prepare for an invasion of the Dutch East Indies, some 140,000 Japanese troops invaded southern French Indochina on 28 July 1941.