On December 7, 1941, Japanese carrier-based aircraft attacked the U.S. naval base at Pearl Harbor in the Hawaiian Islands. The same day, other units launched assaults on the Philippines and began advancing toward the British colony of Malaya. Shortly thereafter, Japanese forces invaded the Dutch East Indies and occupied a number of islands in the Pacific Ocean. In some cases, as on the Bataan peninsula and the island of Corregidor in the Philippines, resistance was fierce, but by the spring of 1942, almost all of Southeast Asia and much of the western Pacific had fallen into Japanese hands. Japan formed the entire region into the Great East Asia Co-Prosperity Sphere and announced its intention to liberate Southeast Asia from Western rule. For the moment, however, Japan needed the resources of the region for its war machine and placed its conquests under its rule on a wartime footing. Japanese leaders had hoped that their strike at American bases would destroy the U.S. Pacific Fleet and persuade the Roosevelt administration to accept Japanese domination of the Pacific. The American people, in the eyes of Japanese leaders, had been made soft by material indulgence. But the Japanese had miscalculated. The attack on Pearl Harbor galvanized American opinion and won broad support for Rooseveltís war policy. The United States now joined with European nations and Nationalist China in a combined effort to defeat Japanís plan to achieve hegemony in the Pacific. Believing that U.S. involvement in the Pacific would render its forces ineffective in the European theater, Hitler declared war on the United States four days after Pearl Harbor.