The United States entered World War II in 1941, following the attack on Pearl Harbor by Japan on December 7. This surprise military strike led to a significant shift in public opinion, as isolationism gave way to the desire for involvement in the war. The day after the attack, President Franklin D. Roosevelt delivered a speech to Congress, describing December 7th as "a date which will live in infamy." As a result, Congress declared war on Japan, officially marking the U.S. entry into the global conflict, which would ultimately see the nation play a crucial role in both the European and Pacific theaters of the war.