What event prompted U.S. entry into World War II?

• A. The Japanese attack on Pearl Harbor on December 7, 1941.
• B. Germany's invasion of Poland.
• C. The attack on Pearl Harbor by Italy.
• D. The signing of the armistice in 1918.

Answer: (A)

Japan's surprise attack on Pearl Harbor on December 7, 1941, pulled the United States into World War II. That assault on the naval base showed that the U.S. could no longer remain neutral while Axis powers expanded their aggression, prompting Congress to declare war on Japan the next day. Soon after, Germany and Italy declared war on the United States, bringing the nation fully into the global conflict. The other events mentioned don’t fit the moment of U.S. entry: Germany’s invasion of Poland started World War II in Europe, but the United States had not entered the war yet; the attack at Pearl Harbor was executed by Japan, not Italy; and the armistice of 1918 ended World War I, long before World War II.