Approximately 250,000 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. 137 Czechoslovakian civilians were killed and 500 seriously wounded during the occupation.

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.