America officially joined World War II on December 8, 1941, the day after the Japanese attack on Pearl Harbor on December 7, 1941. President Franklin D. Roosevelt declared war on Japan in his "Day of Infamy" speech to Congress, which led the United States to enter the conflict formally. Shortly after, on December 11, 1941, Germany and Italy declared war on the U.S., bringing America fully into the global war against the Axis powers.