The united states entered world war II because: Japan attacked Pearl Harbor. - Apex!

Answer: Correct, the United States was neutral at the time.

Explanation: "The attack on Pearl Harbor was a surprise, preemptive military strike by the Imperial Japanese Navy Air Service upon the United States (a neutral country at the time) against the naval base at Pearl Harbor in Honolulu, Territory of Hawaii, just before 08:00, on Sunday morning, December 7, 1941. The attack led to the United States' formal entry into World War II the next day. The Japanese military leadership referred to the attack as the Hawaii Operation and Operation AI, and as Operation Z during its planning."