The correct answer is it ended political divisions between the isolationists and interventionists.
Before the attack on Pearl Harbor, Congress was divided on whether or not the US would enter World War II. Many opposed intervention, as they felt it was Europe's problem to deal with and that the US had to focus on recovering from the Great Depression. Others felt intervention was necessary because the rise of fascim in Europe directly threatened American ideals and trade.
However, this division ended when the Japanese military bombed the US military base at Pearl Harbor on December 7, 1941. One day after this attack, Congress voted to officially enter World War II by an almost unanimous vote.
