The chain of causation

WWII ends with the U.S. and USSR as the only remaining great powers

Disagreements over postwar Europe, particularly the fate of Poland, produce early tensions

Soviet Union imposes communist regimes across Eastern Europe; U.S. responds with containment policy

Communist victory in China (1949) extends the contest to East Asia

Korean War (1950-53) demonstrates that the Cold War could turn hot through proxies

Nuclear arms race produces the doctrine of Mutually Assured Destruction

Cuban Missile Crisis (1962) brings the world to the brink of nuclear war

Vietnam War (1955-1975) becomes the most consequential proxy conflict

Détente in the 1970s produces partial relaxation; renewed tension in early 1980s

Gorbachev's reforms after 1985 unintentionally trigger the collapse of communism in Eastern Europe (1989) and the USSR (1991)