United States' entry into World War II

The results of the attack on Pearl Harbor were many and significant.

On December 7, 1941, the Japanese launched a surprise attack on the U.S. naval base at Pearl Harbor. After two hours of bombing, 18 U.S. ships were sunk or damaged, 188 U.S. aircraft were destroyed, and 2,403 men were killed.

The day after the attack, President Franklin D. Roosevelt addressed a joint session of the 77th United States Congress. Roosevelt called December 7 "a date which will live in infamy". Congress declared war on the Empire of Japan amid outrage at the attack, the deaths of thousands of Americans, and the late delivery of the note from the Japanese government breaking off relations with the U.S. government. Pacifist Representative Jeannette Rankin, a Republican from Montana, cast the only dissenting vote. Roosevelt signed the declaration of war later the same day. Continuing to intensify its military mobilization, the U.S. government finished converting to a war economy, a process begun by provision of weapons and supplies to the Soviet Union and the British Empire. Japanese Americans from the West Coast were sent to internment camps for the duration of the war.

The attack on Pearl Harbor immediately galvanized a divided nation into action. Public opinion had been moving towards support for entering the war during 1941, but considerable opposition remained until the attack. Overnight, Americans united against the Empire of Japan in response to calls to "Remember Pearl Harbor." American solidarity in the war effort probably made possible the unconditional surrender position later taken by the Allied Powers. Some historians, among them Samuel Eliot Morison, believe the attack doomed Imperial Japan to defeat simply because it awakened the "sleeping giant", regardless of whether the fuel depots or machine shops had been destroyed or even if the carriers had been caught in port and sunk. U.S. industrial and military capacity, once mobilized, was able to pour overwhelming resources into both the Pacific and Atlantic theaters. Others, such as Clay Blair, Jr., and Mark Parillo believe Japanese trade protection was so incompetent that American submarines alone might have strangled Japan into defeat.

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