History of Hawaii
Pearl Harbor was surprisingly attacked on December 7, 1941 by the Imperial Japanese Navy, killing 2,403 people and sinking the main American battleship fleet. Fortuitously, the four Pacific aircraft carriers were not in port and escaped damage. Hawaii was put under martial law until 1945. Unlike the West Coast of the United States in which 100,000 ethnic Japanese citizens were interned, the Japanese American population in Hawaii completely avoided such similar fate, though hundreds of pro-Japan leaders were arrested. Pearl Harbor was the U.S.' main forward base for the Pacific War. The Japanese tried to invade in summer 1942 but were defeated at the Battle of Midway. Hundreds of thousands of American soldiers, sailors, Marines, and airmen passed through on their way to the fighting.
Pearl Harbor
Following the overthrow of the Hawaiian Kingdom, the United States Navy established a base on the island in 1899. On December 7, 1941, the base was attacked by the Imperial Japanese Navy airplanes and midget submarines, causing the American entry into World War II. One of the main reasons that Pearl Harbor happened was because the United States had major communication breakdowns among several branches of the U.S. armed services and departments of the U.S. government. This led to the surprise Japanese attack at the Hawaiian air base. There was no meaningful plan for the air defense of Hawaii, for American commanders had no understanding of the capabilities and proper employment of air power. As it was, had the Pacific Fleet acted on the war warnings it undoubtedly would have sortied and been at sea on December 7, where the major ships would have been sunk in deep water, making salvage impossible. 
Shortly after the devastating Japanese surprise attack at Pearl Harbor two American military commanders, Lt. Gen. Walter Short and Adm. Husband Kimmel were demoted of their full ranks. The two American commanders later sought to restore their reputations and full ranks.