What event on December 7, 1941, led to the US entering World War II?

The event on December 7, 1941, that led to the U.S. entering World War II was the attack on Pearl Harbor. This surprise military strike by the Imperial Japanese Navy aimed at the U.S. naval base in Hawaii resulted in significant damage to the Pacific Fleet, including the destruction of battleships and the loss of hundreds of lives. The attack galvanized public opinion in the United States, which had been largely isolationist prior to this event. As a direct response to the attack, the U.S. declared war on Japan the following day, thereby formally entering World War II. This pivotal moment marked a significant shift in the war's dynamics, as it brought the industrial and military resources of the United States into the conflict, significantly impacting the outcome of the war.