In this setting , the Cold War emerged from a conflict between Stalin and U.S. President Harry S. Truman over the future of Eastern Europe during the Potsdam Conference in 1945 . Truman charged that Stalin had betrayed the agreement made at the Yalta Conference . With Eastern Europe under Red Army occupation , the Soviet Union remained adamant in the face of Truman 's attempt to stop Communist expansion , and in 1955 Moscow introduced the Warsaw Pact to counterbalance the Western NATO alliance
Potsdam Conference
Potsdam Conference
Military history of the Soviet Union