Yes, that’s all true, but also see my #70 above re why firing Kennedy still ranks as small beer, imho.
Yalta was in February 1945. At that time the Red Army had overrun all of Eastern Europe and was 40 miles from Berlin. On the other hand, the Anglo-American armies were on the western border of Germany, having just restored what they lost in the Battle of the Bulge. Britain and the US were in no position to demand Stalin withdraw.
Stalin agreed to guarantee the independence of Eastern Europe and to give Britain and the US zones of occupation in areas it was not clear we would conquer before the end of the war. That was the most we could achieve given the cards dealt.
Now, I agree FDR was a dyed in the wool liberal and a squish on communism. His administration was shot through with Soviet spies. But he didn't give away Eastern Europe because it was not ours to give.