Truman by David McCullough:
When and why the Cold War began—whether with announcement of the Truman Doctrine, or earlier, when Truman first confronted Molotov, or perhaps with the eventual sanction of the Marshall Plan by Congress—would be the subject of much consideration in years to come. But the clearest dividing point between what American policy toward the Soviets had been since the war and what it would now become was George Marshall’s return from Moscow. The change came on April 26, 1947, when Marshall, of all men, reported to Truman what Truman had already privately concluded, that diplomacy wasn’t going to work, that the Russians could not be dealt with, that they wanted only drift and chaos and the collapse of Europe to suit their own purposes.
Chip Bohlen, who had been witness to so much—Molotov’s first call on Truman in the Oval Office, the meetings at Potsdam, Marshall’s pivotal session with Stalin at the Kremlin—said the Cold War could really be traced to the seizure of power by the Bolsheviks in 1917. It had begun then, thirty years before.