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.
Attack on Pearl Harbor
One further consequence of the attack on Pearl Harbor and its aftermath (notably the Niihau incident) was that Japanese American residents and citizens were relocated to nearby Japanese-American internment camps. Within hours of the attack, hundreds of Japanese American leaders were rounded up and brought to high-security camps such as Sand Island at the mouth of Honolulu harbor and Kilauea Military Camp on the island of Hawaii. Eventually, more than 110,000 Japanese Americans, nearly all who lived on the West Coast, were forced into interior camps, but in Hawaii, where the 150,000-plus Japanese Americans composed over one-third of the population, only 1,200 to 1,800 were interned.