There are many factors that led to victory for the Allies on both theatres of the war. In Europe, the nation of Germany was up against the leading industrial from the battlefront(United States of America), the largest army in the world at the time with a dictator with an all or nothing blood thirsty resolve that was unmatched by any leader(USSR), and the strongest navy in the world isolated on an island with a people with a steel hard determination in never surrendering to the Nazis(England) these 3 forces enough spelled trouble for the Germans, and their inability to tame their Japanese allies from provoking US entry into the war meant the end for the Third Reich.
All you have to do is write the answer in your thoughts. But just do all of those in your assignment and check if you have done. If this is not what you are talking about, then it might be that you have to chose what you do most.
