In 1942, Bougainville was invaded by the Japanese in order to provide a support base for the operations elsewhere in the South-West Pacific. The Allied counter-invasion resulted in heavy casualties, beginning in 1943, with full control of the islands not re-established until 1945. After the war the Australian government incorporated Bougainville and the rest of the mandate into the Territory of Papua and New Guinea, the immediate predecessor of present-day Papua New Guinea.