The document summarizes the origins of the Cold War between the United States and Soviet Union following World War II. At conferences in Yalta and Potsdam, the wartime allies agreed to divide Germany and Berlin but had differing visions for postwar Europe. Tensions increased as the Soviet Union established communist governments in Eastern Europe and the US sought to contain Soviet expansion through policies like the Truman Doctrine and Marshall Plan. By 1949 the wartime alliance had dissolved into a state of mutual distrust and hostility between the two new superpowers known as the Cold War.