The United States officially entered World War II on December 7, 1941, following the Japanese attack on Pearl Harbor in Hawaii. This surprise military strike caused significant loss of life and damage to the U.S. Pacific Fleet, prompting a swift response from the American government. The following day, President Franklin D. Roosevelt delivered his famous "Day of Infamy" speech, urging Congress to declare war against Japan. This marked a significant shift in U.S. foreign policy, as the nation transitioned from isolationism to active involvement in the global conflict, contributing to Allied efforts in both the European and Pacific theaters.