The Pacific War, sometimes called the Asia–Pacific War, was the theater of World War II that was fought in Asia, the Pacific Ocean, the Indian Ocean, and Oceania. It was geographically the largest theater of the war, including the vast Pacific Ocean theater, the South West Pacific theater, the South-East Asian theater, the Second Sino-Japanese War, and the Soviet–Japanese War.
The Second Sino-Japanese War between the Empire of Japan and the Republic of China had been in progress since 7 July 1937, with hostilities dating back as far as 19 September 1931 with the Japanese invasion of Manchuria. However, it is more widely accepted that the Pacific War itself began on 7 December 1941, when the Japanese invaded Thailand and attacked the British colonies of Malaya, Singapore, and Hong Kong as well as the United States military and naval bases in Hawaii, Wake Island, Guam, and the Philippines.
The Pacific War saw the Allies pitted against Japan, the latter aided by Thailand and to a lesser extent by the Axis allies, Germany and Italy.