What event led to the United States' entry into World War II in 1941?

The attack on Pearl Harbor was the pivotal event that led to the United States' entry into World War II in 1941. On December 7, 1941, Japan launched a surprise military strike against the naval base at Pearl Harbor in Hawaii. This attack resulted in significant destruction of the Pacific Fleet, with numerous ships sunk and thousands of American servicemen killed or wounded.

The immediate impact of this attack unified public opinion in the United States, which had previously been divided over involvement in the war. The event galvanized the nation and prompted President Franklin D. Roosevelt to ask Congress for a declaration of war against Japan, which was granted on December 8, 1941, marking the official entry of the United States into World War II.

The other events mentioned, such as the bombing of Hiroshima, the sinking of the Lusitania, and the invasion of Poland, were historically significant but did not directly lead to the U.S. declaring war in 1941. The sinking of the Lusitania occurred during World War I and contributed to public sentiment against Germany but was not an immediate cause for U.S. involvement in World War II. The invasion of Poland in 1939 marked the beginning of World War II in Europe but did not involve