The liberalisation and democratisation efforts of Alexander Dubchek and Czechoslovakia's Communist Party, known as Prague Spring, took place in 1968. As the Soviet Union thought that Czechoslovakia was moving away of communism, an alliance of Warsaw Pact countries (Soviet Union, Bulgaria, Poland, and Hungary) invaded Czechoslovakia on August 20-21, 1968. Immediately after the invasion, a series of protests took place in Czechoslovakia. 