At Yalta, Roosevelt, Churchill and Stalin all agreed on a peaceful post-war future... At the same time Churchill was working on plans to use all the retreating Nazi troops, as part of an immediate new attack upon Russia - Operation Unthinkable. I think it was there, that Stalin confronted Churchill about the planned betrayal. Churchill denied it.
A few months later Roosevelt was dead, Stalin was convinced he was murdered. Churchill and Truman went forward with the anti-Soviet plans, just more covertly. Patton was loudly complaining that we shouldn't have stopped moving East at Berlin. And then we incorporated Reinhard Gehlen's Eastern European Nazi Intelligence network into the remains if rhe OSS, to create the CIA. The Gehlen network became the Operations Division.