A lot of good and correct answers here. The obvious reason is because Japan attacked Pearl Harbor in Hawii on December 7, 1941. Japan also attacked China in 1937 and at that time, the US sent pilots and planes to China to help the Chinese fight the Japanese.
At this time, The US started to embargo parts and oil to Japan. This increased tensions leading up to December 7, 1941. Up until Pearl Harbor, the US was officially neutral in World War II in Europe, but was sending material to Great Britain.
The japanese launched a surprise attack on the US Pacific Fleet at pearl Harbour, Hawaii, and other US military forces in the pacific on 7 December 1941. On 11 December, Germany and Italy declared war on USA. So, US didn't have much choice about getting involved in WW2.
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.