1. The Cold War began after WWII as tensions grew between the US and USSR, who had different economic and political ideologies of capitalism vs communism. 2. At the Yalta Conference in 1945, the Allied powers agreed to divide Germany into occupation zones and allow free elections in Eastern Europe, but had no agreement on Poland, foreshadowing future tensions. 3. In response to communist influence spreading across Eastern Europe and the Soviet blockade of West Berlin, the US established programs like the Marshall Plan to rebuild Western Europe economically and the Truman Doctrine to contain communism militarily, as well as the NATO alliance for collective defense.