The Philippines had been part of the American commonwealth since it was ceded by Spain at the close of the Spanish-American War. When the Japanese invaded China in 1937 and signed the Tripartite Pact with fascist nations Germany and Italy in 1940, the United States responded by, among other things, strengthening the defense of the Philippines. General MacArthur was called out of retirement to command 10,000 American Army troops, 12,000 Filipino enlisted men who fought as part of the U.S. Army, and 100,000 Filipino army soldiers, who were poorly trained and ill prepared. MacArthur radically overestimated his troops' strength and underestimated Japan's determination. The Rainbow War Plan, a defensive strategy for U.S. interests in the Pacific that was drawn up in the late 1930s and later refined by the War Department, required that MacArthur withdraw his troops into the mountains of the Bataan Peninsula and await better-trained and -equipped American reinforcements. Instead, MacArthur decided to take the Japanese head on--and he never recovered.
On the day of the Pearl Harbor bombing, the Japanese destroyed almost half of the American aircraft based in the Philippines. Amphibious landings of Japanese troops along the Luzon coast followed. By late December, MacArthur had to pull his forces back defensively to the Bataan Peninsula--the original strategy belatedly pursued. By January 2, 1942, the Philippine capital of Manila fell to the Japanese. President Roosevelt had to admit to himself (if not to the American people, who believed the Americans were winning the battle with the Japanese in the Philippines), that the prospects for the American forces were not good--and that he could not afford to have General MacArthur fall captive to the Japanese. A message arrived at Corregidor on February 20, ordering MacArthur to leave immediately for Mindanao, then on to Melbourne, Australia, where "You will assume command of all United States troops." MacArthur at first balked; he was fully prepared to fight alongside his men to the death if necessary. MacArthur finally obeyed the president's order in March.