First of all one came first, then the other came second, but that is fairly obvious. World war I was fought by the Allies and the Central Powers. World war II was fought with the Allies and the Axises.
The participants within the war also changed. Italy for example switched sides from the Allies in WWI to the Axises in WWII. Japan also followed this same pattern.
Those are two large differences between the two wars.
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.