The notorious event in U.S. history that occurred on December 7, 1941, leading the U.S. into World War II, was the attack on Pearl Harbor. This surprise military strike by the Imperial Japanese Navy targeted the U.S. naval base in Hawaii, resulting in significant loss of life and damage to the Pacific Fleet. The attack galvanized American public opinion and unified the nation behind the war effort. Subsequently, the U.S. declared war on Japan, marking its formal entry into World War II and altering the course of the conflict.