Czechoslovakia had been a communist country, controlled by Moscow, since the end of World War Two. In 1968 the Czech people attempted to exert some control over their own lives and reform the Communist system to create 'Socialism with a human face'. That meant keeping the socialist model of government but guaranteeing a better delivery of goods, services and freedoms to the Czech people. This attempt, known as the Prague Spring, lasted for four months until it was crushed by the Soviet Red Army.
In 1967 Czech students began peacefully demonstrating against Novotny’s rule. Novotny asked the Soviet leader, Brezhnev, for help to crackdown on the protests, but Brezhnev refused, and in early 1968 Novotny was replaced as Communist Party Secretary by Alexander Dubcek.
In April 1968, Dubcek announced an Action Plan to deliver 'Socialism with a Human Face’ which, in a nutshell, meant removing state control of the economy and allowing freedom of speech.
Dubcek’s reforms began to worry the Soviets because although he claimed to be a committed communist, Dubcek proposed allowing non-communist political parties to be set up and to put up candidates for election. Also Dubcek said that Czechoslovakia would remain in the Warsaw Pact, but then welcomed Marshal Tito, President of Yugoslavia, to Prague. Yugoslavia had been communist since World War Two but was not a member of the Warsaw Pact and Moscow was wary of Tito.
As in Hungary in 1956, the Western powers did nothing to actively support the Czechs in their ‘Prague Spring’. The US accepted that the Soviets were taking this action in their own sphere of influence, and the US was not going to consider any intervention that would constitute roll back of communism in Eastern Europe.