When did the Americans enter ww11?

The United States entered World War II on December 7, 1941, following the Japanese attack on Pearl Harbor. This surprise military strike led to the U.S. declaring war on Japan the next day, December 8, 1941. Subsequently, Germany and Italy declared war on the U.S. on December 11, 1941, prompting the U.S. to join the conflict against the Axis powers.