How did the united states and the soviet union become cold war adversaries?

The Cold War shaped much of world history over the next four
decades after the end of World War II. The Allies argued over the postwar settlement. The United States, Britain, and Russia met at the Teheran Conference in 1944. The decision for an invasion of France left Russia free to move into eastern Europe. The three met again at Yalta in 1945. The Soviet Union agreed to join against Japan in return for territorial gains in China and Japan. The United Nations was confirmed. Agreement over Europe's future was difficult. A disarmed Germany, purged of Nazi influence, was divided into four occupied zones. Eastern Europe, although promises were made for a democratic future, was left under Soviet domination.