On December 7th, 1941, the Japanese attack Peral Harbor in Hawaii. The Japenese attack the United States because they decided they didn't want to proceed with trading. The United States also broke their code of communication which, led them to know they were going to be attacked. The bombings led the United States to enter World War II.
Congress agrees with FDR to declare war on Japan.
The US offically enters WWII while being apart of the allied powers, after Germany and Italy declared war.