What event triggered the United States' entry into World War II?

The event that triggered the United States' entry into World War II was the attack on Pearl Harbor on December 7, 1941. This surprise military strike by the Imperial Japanese Navy against the U.S. naval base in Hawaii resulted in significant loss of life and damage to the Pacific Fleet, leading to widespread outrage among the American public and a unified call for action against Japan. As a result, the United States declared war on Japan the following day, December 8, 1941, marking the official entry of the U.S. into World War II.

This event changed the course of the war for the U.S. and its allies, as it mobilized American military and economic resources, which had previously been focused on isolationist policies and supporting allies through programs like Lend-Lease. The attack on Pearl Harbor is often seen as a pivotal moment in U.S. history that galvanized public opinion and shifted the nation from a stance of neutrality to active involvement in global conflicts.

Other events listed, such as the sinking of the Lusitania or the invasion of Poland, though significant in their own contexts, did not lead to a direct U.S. declaration of war. The Lusitania incident in 1915 contributed to anti-German sentiment before