December 8, 1941 - The day after Pearl Harbor was attacked by the Japanese, the United States of America declared war on the Axis powers. Source: wiki.answers.com/Q/When_did_the_US_enter... Pic source: t0.gstatic.com/images?q=tbn:ANd9GcTipJCt....
Different countries joined at different dates.
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.