Once again the world found itself in large-scale multinational conflict. This world war involved two primary theatres of combat, the Asian theatre, and the European Theatre. This just means where the fighting took place. The main powers at war were Germany, Italy, and Japan for the Axis Powers, and the United Kingdom, Soviet Union, and China made up the Allies. The United States would join the Allies later in the war. There were many things that lead to the war and much depends on viewpoint. It is clear that a key component was the rise of Nazi Germany led by Adolph Hitler. And the invasion of Poland sealed the march to a world war.