What event in 1941 caused the US to join the Allies in WWII?

Japan’s attack on Pearl Harbor on December 7, 1941, led the United States to declare war on Japan the next day. The United States then entered the war alongside the Allies. Germany’s invasion of the USSR and its capture of France occurred before 1941, and Italy’s move into North Africa was not the event that brought the United States into the war.

AI-written and checked against the verified answer.