Japan invaded China USA didn't like that and decided to put sanctions on Japan and had most other western countries do the same. 90% of Japan's oil was halted. Japan saw this as an aggressive act so they attacked Pearl Harbor USA then officially attacked Japan.
Formally -- the US entered the war after the Japanese attack on Pearl Harbour in Dec 1941. Before that however , during 1940 and 1941, the US actively supported Britain and her allies by providing them with arms and other supplies ,and later provided protection to these supply convoys ,against U Boat patrols, in the western Atlantic.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.