Apparently you are viewing some other history than that of planet Earth. On planet Earth the US and the USSR were allies and the former supplied the latter to fight the Nazis. They made plans together and fought the common enemy.
There was no way that the American people would have supported a war against their ally in 1945 and millions of Soviet soldiers were not going to allow any but a long and bloody fight to force them back from the territory it had conquered. We certainly did not have the men there to do is and Stalin knew we had no more A bombs. So this fantasy is right up there with the one about the secret Nazi base at the South Pole or on the Moon.
Just because the free world ended up with a common enemy...to call them our "ally" is a reality stretch.
Had the Russian military not been battered so completely and the western allies by pact had been weakened sufficiently Russia WOULD have continued her push west.
Only a very naive individual or a Democrat politician the likes of Jimmy Carter could perceive otherwise.