The Pacific War, sometimes called the Asia-Pacific War, was the theater of World War II that was fought in the Pacific and Asia. It was fought over a vast area that included the Pacific Ocean and islands, the South West Pacific, South-East Asia, and in China.
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 7/8 December 1941, when Japan invaded Thailand and attacked the British possessions 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 briefly aided by Thailand and to a much lesser extent by the Axis allied Germany and Italy.