The Soviets defeated the Germans in winter of 1942/1943 at Stalingrad where they lost far too many men to have a shot at winning the war, and the main German army was completely destroyed. At that point the war was over, there was nothing the Germans could do on the Eastern front. America invading in the western front had no impact on the outcome of the war, only in the cold war after ww2. There was only one actual battle fought on the western front, and the Americans got completely steamrolled by the more experienced Germans (most American troops were hastliy trained and shiped out, where as most German troops had been fighting for several years, they were as experienced if not more so than our combat troops in Afghanistan), until the Germans ran out of fuel for their tanks and had to retreat.
Lots of people in America have this impression that America played a huge part in the war and dominated the German army, when that was not the case at all. This impression has been gotten from TV and movies made about the war, and the jobs of these tv/film makers is to make money not tell the truth, oh but it says based on a real story, how many movies about monsters and ghosts have you seen say that. Obviously people would not want to see a realistic portraly of ww2 in a movie as people want to see their team win decisively. Even D-Day is blown way out of proportion and grossly exaggerated, the Americans were successful in tricking the Germans into thinking they would land somewhere else so the Germans barely had any forces on the beaches that were attacked, and it was a relatively quick and easy victory for the allies with their superior forces.
But that was the main American strategy during the war, show up to a German defensive position with overwhelming force such that the German soldiers would just surrender as there was no point getting killed as they knew they had already lost the war 2 years ago and they knew that the Americans treated the German POWs very well. And thats a very good strategy, you win the fight without losing any men or equipment, and treating your PoWs well encourages the enemy soliders to surrender, many germans would have rather died than surrender to the Russians. Better to die fighting than freeze/starve to death in a russian concentration camp as 60% of german pows did.
And the soviets did not win Stalingrad because of the "lend lease program" which almost all of the funding for went to the British not the soviets. The germans were not able to take the city in time and the russians would not give up, and einstein would not allow his generals to retreat for the winter as they had wanted to. So they were forced into a seige in Russia in the winter time and the cold broke down the army in a number of ways.
