Final answer:
The attack that caused the United States to enter World War II was the attack on Pearl Harbor.
Step-by-step explanation:
The attack that caused the United States to enter World War II was the attack on Pearl Harbor. On December 7, 1941, Japanese forces launched a surprise attack on the U.S. naval base in Pearl Harbor, Hawaii. This attack led to the United States declaring war on Japan and entering World War II.
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