Success against Nazi Germany gave the U.S.S.R. supremacy in Europe after WWII, and by default of the cataclysmic destruction of other combatants in the world, the ability to challenge American hegemony. With the largest armies in the world positioned in Eastern Europe, the U.S.S.R. was in no position to leave, nor would it, given Germanys history of invading Russia. Yet it wasnt just armies that allowed the U.S.S.R. to challenge the U.S. Economic power also gave the Soviets an advantage. After the war, communist economic planning had built a vast, modern industrial infrastructure. It was the biggest reason for the defeat of Nazi Germany; it could also rival the U.S. economic ambitions in Europe.