Why did the United States enter World War II?

What does this answer mean?

The United States entered World War II because Japan attacked Pearl Harbor. USCIS accepts four answers: the bombing of Pearl Harbor; the Japanese attacked Pearl Harbor; to support the Allied Powers (England, France, and Russia); or to oppose the Axis Powers (Germany, Italy, and Japan).

On December 7, 1941, Japanese aircraft attacked the American naval forces at Pearl Harbor, Hawaii. The next day, President Franklin D. Roosevelt spoke to Congress, calling December 7 "a date which will live in infamy," and Congress declared war on Japan. On December 11, Germany and Italy declared war on the United States.

The war had already been going on in Europe and Asia for years. Once the United States entered, it fought with the Allied Powers against the Axis Powers until the war ended in 1945.

General Dwight Eisenhower, who led the Allied forces that invaded France on D-Day in 1944, is the subject of the next question.

At the interview, say "the Japanese attacked Pearl Harbor."