The fate of Post WWII Europe was largely determined by FDR’s disastrous concessions to Stalin in Yalta.
We could,however, have done much more to prevent the Russian takeover of Eastern Europe and we should have done so.
Stalin was very dependent upon American aid to keep his Army going and his troops in Eastern Europe were very extended with long supply lines.
The West basically rolled over politically to Stalin and Socialists governments very sympathetic to the Soviets were elected in Great Britain and in much of Europe because there just was no political will to resist Stalin.
Militarily, the cost would have been very high to go against the Soviets.
The allies gave nothing away. Stalin had the whip hand and was not going to release it.
FDR was a sick pup at Yalta.
Many believe he was going through the motions and wanted to get back to Warm Springs.
Yes, these were the Russians the Democrats and liberals loved - the ones they now hate, strangely.