Introduction to the Cold War
The Cold War is a term used to describe a period of rivalry and suspicion between the United States and the Soviet Union after the Second World War.

Source: https://www.foreignaffairs.com/reviews/review-essay/2022-04-06/cold-war-never-ended-russia-ukraine-war
After 1945 both the United States and the Soviet Union became superpowers. The spheres of influence they constructed (blocs) were surprisingly symmetrical. On the military level, the Soviet Union created the Warsaw Treaty Organization (WTO) in response to creating the North Atlantic Treaty Organization (NATO) in the West. On the economic level, the Soviet Union established a trade organization called CMEA which could be considered the counterpart of financial organizations in the West, such as the European Economic Communities (EEC) and the Organization for Economic Cooperation and Development) OECD.
Each bloc had its ideological mission, networks of alliances and third-world clients, and deadly nuclear weapons arsenal. Europe was divided, with massive military forces of the United States and its NATO allies on one side and massive forces of the Soviet Union and its Warsaw Pact allies on the other. Germany was split, with three-quarters of the country (and three-quarters of the city of Berlin) occupied by the United States, Britain, and France. The remainder, surrounding West Berlin, was occupied by the Soviet Union.
In 1961 East Germany built the Berlin Wall separating East from West Berlin. It symbolized the division of Europe by what Winston Churchill had called the “iron curtain.” Despite the hostility of East-West relations during the Cold War, a relatively stable framework of relations emerged, and conflicts never escalated to all-out war. The central concern of the West during the Cold War was that the Soviet Union might gain control of Western Europe- either through invasion or through communists’ taking power in war-weary and impoverished Western European countries.

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Through the policy of containment, the U.S. sought to halt the expansion of Soviet influence globally on several levels- military, political, ideological, and economic. The Cold War thawed temporarily when Stalin died in 1953. Still, hostilities increased after Khrushchev was removed from power, culminating in the Cuban Missile Crisis of 1962, when the Soviet Union installed medium-range nuclear missiles in Cuba. U.S. President Kennedy imposed a naval blockade to force their removal. The USSR backed down on the missiles, and the United States promised not to invade Cuba in the future. The possibility of nuclear war shook leaders on both sides.
In retrospect, it seems both superpowers had exaggerated Soviet strength. Behind the military parity lay the Soviet Union, which lagged far behind the West in everything else- wealth, technology, infrastructure, and citizen/worker motivation.
Scholars disagree on the question of why the Cold War ended. One line of argument holds that U.S. military strength under President Reagan forced the Soviet Union into bankruptcy as it tried to keep up in the arms race. Another view holds that the Soviet Union suffered from internal stagnation over several decades and ultimately imploded because of weaknesses in its system of governance that had little to do with external pressure. Indeed, some scholars think the USSR would have fallen apart much earlier if it had not been for the U.S. as a foreign enemy whose unintentional role was to bolster the Soviet government’s legitimacy with its people.