Pacific War, major theatre of World War II that covered a large portion of the Pacific Ocean, East Asia, and Southeast Asia, with significant engagements occurring as far south as northern Australia and as far north as the Aleutian Islands. The Japanese war plan, aimed at the American, British, and Dutch possessions in the Pacific and in Southeast Asia, was of a rather makeshift character. The first draft, submitted by the chiefs of the Army and Navy General Staff, was accepted by Imperial General Headquarters early in September 1941. The lateness of the draft was due largely to the long