Pacific War

The Pacific War, sometimes called the Asia–Pacific War or the Pacific Theatre, was the theatre of World War II fought between the Empire of Japan and the Allies in East and Southeast Asia, the Pacific and Indian Oceans, and Oceania. It was geographically the largest theatre of the war, including the Pacific Ocean theatre, the South West Pacific theatre, the Second Sino-Japanese War, and the brief Soviet–Japanese War, and included some of the largest naval battles in history. War between Japan and the Republic of China had begun in 1937, with hostilities dating back to Japan's invasion of Manchuria in 1931, but the Pacific War is more widely accepted to have started in 1941, when the United States and United Kingdom entered the war against Japan.

Japan invaded French Indochina in 1940, and extended its control over the entire territory in July 1941. On 7–8 December 1941, Japan attacked the American naval base at Pearl Harbor in Hawaii; the U.S.-held Philippines, Guam, and Wake Island; and the British colonies of Malaya, Singapore, and Hong Kong, resulting in declarations of war. The Japanese achieved great success over the next six months, allying with Thailand and capturing the listed territories (except for Hawaii) in addition to Borneo, New Britain, the Dutch East Indies, Burma, the Solomon and Gilbert Islands, and parts of New Guinea. In May 1942, Japanese and Allied aircraft carriers fought at the Battle of Coral Sea, resulting in the retreat of a Japanese invasion force headed for Port Moresby. In June, Japan invaded the Aleutian Islands, and in the central Pacific was defeated at the Battle of Midway, considered a key turning point in the war. After this point, the Japanese experienced great difficulty replacing their losses in ships and aircraft as the U.S. produced ever increasing numbers of both.

Major Allied offensives in the Pacific began in August 1942 with the Guadalcanal and New Guinea campaigns. These were followed by Operation Cartwheel from June 1943, which neutralized the major Japanese base at Rabaul on New Britain by early 1944. Elsewhere, Allied forces recaptured the Aleutian Islands by August 1943, and initiated the Gilbert and Marshall Islands campaign in November 1943, which lasted until February 1944. In the Battle of the Philippine Sea in June 1944, the Japanese fleet took heavy damage; the Allied campaign to recapture the Philippines began in October and set off the Battle of Leyte Gulf, after which the Japanese were unable to fight further surface engagements and resorted to kamikaze attacks. The rest of the war was characterized by an Allied strategy of island hopping, with invasions of the Mariana and Palau Islands, Iwo Jima, and Okinawa between June 1944 and June 1945. This enabled a blockade of the Japanese home islands and the start of a strategic air raid campaign which caused widespread urban destruction.

In China, Japan made large gains in Operation Ichi-Go between April and December 1944, while in Burma, the Japanese launched an offensive into India which was reversed by July 1944 and led to its liberation by the Allies in May 1945. From the start of the war, the Allies had adopted a "Europe first" stance, giving priority to defeating Germany; after Germany's surrender in May 1945, Allied forces were shifted to the Pacific in anticipation for Operation Downfall, a planned invasion of Japan. This became unnecessary after the U.S. atomic bombings of Hiroshima and Nagasaki on 6 and 9 August 1945 and Soviet invasion of Manchuria on 9 August, after which Japan surrendered unconditionally on 15 August and signed a surrender document on 2 September, ending World War II. Japan lost its former possessions in Asia and the Pacific, and was occupied by the Allies until 1952.