The Philippines had suffered under the Japanese occupation. A highly effective guerrilla campaign controlled sixty percent of the islands, mostly jungle and mountain areas. United States Army General Douglas MacArthur had supplied them by submarine, and sent reinforcements and officers.
More than any other Allied garrison attacked on December 7, 1941, the Philippines were an important target for the Imperial Japanese High Command. Japanese Navy and Army bombers from Formosa attacked in the late morning, and achieved the same success their comrades were enjoying over Pearl Harbor.
United States Army General Douglas MacArthur planned to prevent attacks in his rear area during the reconquest of the Philippines by taking the Morotais and the Palaus. The most heavily defended island in the Palaus was Peleliu. He felt that he need to hold Peleliu before he could move on the Philippines.
When General Douglas MacArthur arrived in Australia after evacuating Bataan, he was a General in search of an offensive army. The Americans did not yet have a fighting force in the Pacific, and the Australians were committed in North Africa, en route to Pacific stations, or in training or garrison in Australia.
United States Army General Douglas MacArthur had fought a hard campaign up the back of New Guinea, only to see his greatest successes eclipsed in the press by the invasions in the central Pacific and Europe. Privately, he was considering a run for US President against Roosevelt, and he did not get along with United States Navy Admiral Chester Nimitz.