When and why did the US enter World War 2?

the US joined WWII because of the attack on pearl harbor which took place 7th of December, 1941, the US joined quickly after that
America joined WW2 shortly after the Pearl Harbor bombing. Japan and the US were on hot ground, fighting over oil pipes in Japan.
In December 1941, after the Japanese attacked Pearl Harbor resulting in the loss of several ships and the deaths of 2,000 sailors, despite the fact the nations were not at war with each other. Japan was anticipating war with the US, especially after the Americans stopped supplying oil and moved their Pacific fleet to Hawaii.