Which event shattered the us policy of neutrality during world War 2?

The event that shattered the U.S. policy of neutrality during World War II was the attack on Pearl Harbor by Japan on December 7, 1941. This surprise military strike led to significant loss of life and damage to the U.S. Pacific Fleet, prompting Congress to declare war on Japan the following day. Subsequently, Germany and Italy declared war on the United States, fully committing the nation to the conflict. This marked a decisive shift from isolationism to active involvement in the war.