When the U.S. heard that the Japanese were stealing oil, the US had to stop it. The Japanese military was asked to make a war plan. They proposed a sweep into Burma, Malaya, and the Philippines and also establishing a defensive boundary of the Central and Southwest Pacific. They expected the US to declare war but not be willing to fight long or hard enough to win. Their greatest concern was the Pacific fleet in Pearl Harbor, and they were going to surprise attack Pearl Harbor.