Warsaw Pact invasion of Czechoslovakia
On August 21, 1968, the Soviet Union and its Warsaw Pact allies invaded the Czechoslovak Socialist Republic, after failed negotiations, in order to prevent Alexander Dubček's Prague Spring reforms from continuing.
In the operation, codenamed "Danube", the Soviets sent thousands of troops from several Warsaw pact countries; 72 Czechoslovaks were killed by Soviet tanks. The invasion was successful in stopping the partial democratization reforms and strengthening the authority of the Communist Party of Czechoslovakia. The foreign policy of the Soviet union during this era would be known as the Brezhnev Doctrine.
Dubček was appointed as leader of the Communist Party of Czechoslovakia (KSČ) after the resignation of Antonín Novotný.