The Philippines campaign, Battle of the Philippines, Second Philippines campaign, or the Liberation of the Philippines, codenamed Operation Musketeer I, II, and III, was the American, Mexican, Australian and Filipino campaign to defeat and expel the Imperial Japanese forces occupying the Philippines during World War II.
The Japanese Army overran all of the Philippines during the first half of 1942. The liberation of the Philippines from Japan commenced with amphibious landings on the eastern Philippine island of Leyte on October 20, 1944. The United States and Philippine Commonwealth military forces, with naval and air support from Mexico and Australia, were progressing in liberating territory and islands when the Japanese forces in the Philippines were ordered to surrender by Tokyo on August 15, 1945, after the dropping of the atomic bombs on mainland Japan and the Soviet invasion of Manchuria.
By mid-1944, American forces were only southeast of Mindanao, the largest island in the southern Philippines – and able to bomb Japanese positions there using long-range bombers. American forces under Fleet Admiral Chester W. Nimitz had advanced across the Central Pacific Ocean, capturing the Gilbert Islands, some of the Marshall Islands, and most of the Marianas Islands, bypassing many Japanese Army garrisons and leaving them behind, with no source of supplies and militarily impotent.
Aircraft carrier-based warplanes were already conducting air strikes and fighter sweeps against the Japanese in the Philippines, especially their military airfields. U.S. Army and Australian Army troops under the American General Douglas MacArthur, the Supreme Commander of the Southwest Pacific Theater of Operations, had either overrun, or else isolated and bypassed, all of the Japanese Army on New Guinea and the Admiralty Islands. Before the invasion of the Philippines, MacArthur's northernmost conquest had been at Morotai in the Dutch East Indies on September 15–16, 1944. This was MacArthur's one base that was within bomber range of the southern Philippines.