What was the primary factor in America entering World War II?
the resumption of unrestricted submarine warfare
the passage of the Lend-Lease Act
the renewal of Nazi aggression
a suprise attack on United States soil

Surprise attack on American soil.

Explanation:

On December 7th 1941 Japan bombed an american naval base known as pearl harbor. Pearl Harbor is close to Japan because it is an island far west of the united states but is considered a state. So it was a attack on American soil by the Japanese air force and kamikaze fighters. After the attack Japan and Germany (+ Axis Powers) Declared war on the United States. But according to Hitlers plans to take over the world he wanted to attack north america last. So technically we can thank the Japanese we are still the United States of america and not speaking German.      

sorry i do not know this