Why did the Japanese bomb Pearl Harbor thus starting the War in the Pacific?
The attack on Pearl Harbor on December 7, 1941 was a classic case of winning a battle but losing a war. Although Japan succeeded in its immediate mission of damaging U.S. ships and aircraft, it had the effect of galvanizing United States public opinion in favor of prosecuting a full-on war effort, especially in the east. Isolationist sentiment evaporated the instant people heard news of attacks on United States soil. No longer was World War II a foreign conflict on foreign soil; suddenly it became a matter of defending the United States.
What Japan had intended by the attack on Pearl Harbor, and several associated attacks that took place on the same day in the Philippines, Guam and Wake Island as well as British territories is South East Asia, was to cripple U.S. naval power in the Pacific in a single, massive preemptive blow. Japan had calculated that by crippling U.S. battleship, they would buy enough time to consolidate their positions and make them impregnable.