Which battle during World War II do you believe was more instrumental in defeating Nazi Germany, D-Day or Operation Barbarossa? I'm an American and I'm hesitant to say that either side was more instrumental. On one side the Americans liberated France and on the other side the Soviets pushed back the Germans. Arguably, the Soviets reached Berlin first, but if it wasn't for the American-led invasion in Western Europe, the Germans could have focused all of their attention on the Soviet Union and possibly launched a successful counter-offensive. But without Operation Barbarossa, the Soviet Union would have been severely weakened, and possibly even defeated. Which battle do you think was more instrumental in defeating Nazi Germany?