Nobody except maybe Patton wanted a hot war with the Ruskies after an exhausting two-front world war. Nevertheless, I’m not sure how strongly FDR contended for Berlin at Yalta. I mean the U.S. isn’t interested in permanent occupation but the Ruskies sure were.
It should have been a hard negotiating point IMO, with what intelligence certainly should have known about Stalin’s brutality and millions of Russian deaths at his hands. Good intelligence also should have informed us of Russia’s basic weaknesses - an empty armored shell. Knowing those things should have given us negotiating leverage.
Our disinterest and their great interest probably made a difference, but I think it was a mistake to not try harder for Berlin, if not all of it, at least the western half of Germany running through the middle of Berlin instead of the foreseeable airlifts that had to come later.
Roosevelt was at death’s door at Yalta, and he was surrounded by advisers who were, in my opinion, blind to who and what Stalin really was. To put it in the most charitable light I can, they naively trusted the word and goodwill of a tyrant and mass murderer.