The Cold War (1947-1991)
The defining conflict of the second half of the 20th century - fought everywhere except directly between its two main protagonists.
Origins
The alliance between the USA and USSR was always uneasy, born of necessity against Nazi Germany. By 1947, mutual distrust had hardened into confrontation. The USSR established Soviet-controlled governments across Eastern Europe. The USA responded with the Truman Doctrine (containing Soviet expansion) and the Marshall Plan (rebuilding Western Europe economically). By 1949 both sides had nuclear weapons, dividing the world into two armed camps with incompatible visions of the future.
Nuclear Arms Race
The arms race produced an absurd and terrifying stockpile. By the 1980s the USA and USSR together had 70,000 nuclear warheads - enough to kill every person on Earth multiple times. The doctrine of Mutual Assured Destruction (MAD) argued this was stabilizing: neither side could strike first without being destroyed in retaliation. Critics noted the logic depended on rational actors with perfect information - not always guaranteed in a crisis.
Proxy Wars
The superpowers avoided direct conflict but fought through proxies everywhere. Korea (1950-1953): 36,000 American and 180,000 Chinese deaths. Vietnam (1955-1975): 58,000 American, up to 3 million Vietnamese deaths. Angola, Mozambique, Nicaragua, Afghanistan, and dozens of other countries were battlegrounds for Cold War competition. The Cold War killed more people through proxy conflicts than most "hot" wars in history.
The Cuban Missile Crisis (1962)
The closest the world came to nuclear war. After the Bay of Pigs failure, the USSR secretly placed nuclear missiles in Cuba. American reconnaissance aircraft discovered them on October 14, 1962. For 13 days the world teetered on the edge of annihilation. Kennedy chose a naval blockade over air strikes. Soviet ships turned back. Khrushchev agreed to remove the missiles in exchange for an American pledge not to invade Cuba and a secret removal of US Jupiter missiles from Turkey. Declassified documents show we came far closer to war than was known at the time.
Near-Misses Beyond Cuba
The crisis the world does not know: in September 1983, Soviet Colonel Stanislav Petrov received an alert that the USA had launched five nuclear missiles. The protocol required him to immediately report up the chain for a retaliatory strike. Petrov judged it a false alarm (correctly) and did not report it. He was right - it was a satellite malfunction. One month later the Able Archer NATO exercise was so realistic that Soviet intelligence believed it might be a cover for a real first strike and brought Soviet nuclear forces to high alert.
The End of the Cold War
Mikhail Gorbachev's reforms (glasnost, perestroika) after 1985 were intended to save Soviet communism, not end it. But once the lid was lifted, 70 years of accumulated grievances poured out. Eastern European states broke free in 1989 (Poland, Hungary, Czechoslovakia, East Germany, Romania). The USSR itself dissolved on December 25, 1991 when Gorbachev resigned and the Soviet flag over the Kremlin was replaced by the Russian tricolor. The Cold War ended not with a bang but with a flag being lowered.