The surprise pre-emptive air attack by the Japanese on the American Pacific Fleet in their base at Pearl Harbor in Oahu, Hawaii, on December 7th 1941 had momentous consequences. In a day which President Franklin Roosevelt said would “live in infamy”, the Japanese aircraft sank 18 warships, damaged several more, and killed over 2,400 U.S. personnel. The following day, America declared war on Japan and Germany and Italy quickly responded by declaring war on America. There is some argument about how much of a surprise Pearl Harbor was – tensions between the USA and Japan had been increasing since 1937 and various different intelligence sources knew an attack was imminent by 1941, even if they did not know precisely where or when. However, it is doubtful that Roosevelt deliberately left the fleet open to attack to ensure U.S. entry into the war – as some historians have argued!
American entry into World War II was to have an enormous effect as the U.S. economy moved into gear to provide the Allies with munitions and eventually the manpower that helped secure victory in both Europe and the Pacific, but the war also signaled an end to American isolationism and the rise of the U.S. as a super-power. It could be argued that another consequence of Pearl Harbor was the start of the atomic age – something only the Japanese were to suffer in 1945. But while the long-term international consequences were enormous, the war also effectively ended the depression in America and initiated enormous economic growth leading ultimately to the affluent society at home.