Which forced United States to join World War II?

A. The Invasion of Poland
B. Attack on Pearl Harbour
C. The D-Day Invasion
D. None of these

The attack on Pearl Harbour (B) by Japan on December 7, 1941, directly led the United States to enter World War II, as it prompted a declaration of war against Japan and its allies. The Invasion of Poland (A) occurred in 1939 and involved European powers, not directly the US. The D-Day Invasion (C) happened in 1944, after the US was already in the war. “None of these” (D) is incorrect because B is the correct answer.

Correct Answer: B. Attack on Pearl Harbour