The United States entered World War II on the side of the allies after the Japanese attack on Pearl Harbor on December 7, 1941. Prior to the attack, the U.S. had been providing aid and support to the Allied powers, but was officially neutral in the conflict. After the surprise attack, President Franklin D. Roosevelt declared war on Japan the following day, and three days later, Germany and Italy declared war on the United States. This prompted the U.S. to formally join the Allied powers and engage in the war effort to defeat the Axis powers.
