The correct answer is B) The Japanese attack on Pearl Harbor.
The US was attacked by the Japanese Empire on December 7, 1941. On this day, Japan attacked the US military base in Hawaii, killing thousands of soldiers and civilians. The next day, president Franklin D. Roosevelt went before Congress to ask them to officially declare war on Japan. Congress obliged and as of December 8, 1941 the US was at war against Japan.
The correct answer is B. Although all of the things contributed, the attack on Pearl Harbor was the main reason. This was direct aggression towards the United States and they had no choice but to enter.
