The Warsaw Pact invasion of Czechoslovakia, officially known as Operation Danube, was a joint invasion of Czechoslovakia by five Warsaw Pact countries – the Soviet Union, Poland, Bulgaria, East Germany and Hungary – on the night of 20–21 August 1968.[17] Approximately 250,000[4] Warsaw pact troops attacked Czechoslovakia that night, with Romania and Albania refusing to participate. East German forces, except for a small number of specialists, did not participate in the invasion because they were ordered from Moscow not to cross the Czechoslovak border just hours before the invasion.[1] 137 Czechoslovakian civilians were killed[13] and 500 seriously wounded during the occupation.[14] The invasion successfully stopped Alexander Dubček’s Prague Spring liberalisation reforms and strengthened the authority of the authoritarian wing within the Communist Party of Czechoslovakia (KSČ). The foreign policy of the Soviet Union during this era was known as the Brezhnev Doctrine
