Warsaw Pact invasion of Czechoslovakia

On 20–21 August 1968, the Czechoslovak Socialist Republic was jointly invaded by four fellow Warsaw Pact countries: the Soviet Union, the Polish People's Republic, the People's Republic of Bulgaria, and the Hungarian People's Republic. The invasion stopped Alexander Dubček's Prague Spring liberalisation reforms and strengthened the authoritarian wing of the Communist Party of Czechoslovakia (KSČ). About 250,000 Warsaw Pact troops (rising afterwards to about 500,000), supported by thousands of tanks and hundreds of aircraft, participated in the overnight operation, which was code-named Operation Danube.