During World War II, the United States and the Soviet Union fought together as allies against the Axis powers. However, the relationship between the two nations was a tense one. Americans had long been wary of Soviet communism and concerned about Russian leader Joseph Stalin’s tyrannical. For their part, the Soviets resented the Americans’ decades-long refusal to treat the USSR as a legitimate part of the international community as well as their delayed entry into World War II, which resulted in the deaths of tens of millions of Russians. After the war ended, these grievances ripened into an overwhelming sense of mutual distrust and enmity. Postwar Soviet expansionism in Eastern Europe fueled many Americans’ fears of a Russian plan to control the world. So, U.S. adopted “containment” defense strategy
Two strongest countries in the world, and they didn’t want to war, so the National Security Council: use military force to “contain” communist expansionism
In response to severe economic problems and growing political ferment in the USSR, Gorbachev took office in 1985 and introduced two policies that redefined Russia's relationship to the rest of the world: "glasnost," or political openness, and "perestroika," or economic reform. Soviet influence in Eastern Europe waned. In November 1989, the Berlin Wall–the most visible symbol of the decades-long Cold War–was finally destroyed, just over two years after Reagan had challenged the Soviet premier in a speech at Brandenburg Gate in Berlin: "Mr. Gorbachev, tear down this wall." By 1991, the Soviet Union itself had fallen apart. The Cold War was