In the early 1960s, Czechoslovakia suffered an economic recession. Antonin Novotny, president of the country, was forced to make liberal concessions and in 1965 he introduced a program of decentralization, but it had little impact on economy.
In January 1968, Antonin Novotny was replaced by Alexander Dubcek as party secretary. Dubcek made a speech where he stated: “We shall have to remove everything that strangles artistic and scientific creativeness.” A series of reforms were introduced, which was known as the Prague Spring, including the abolition of censorship and the right of citizens to criticize the government,
The new reform program also included the creation of works councils in industry, increased rights for trade unions to bargain on behalf of its members and the right of farmers to form independent co-operatives.
In July 1968 the Soviet leadership announced that it had evidence that the Federal Republic of Germany was planning an invasion of the Sudetenland and asked permission to send in the Red Army to protect Czechoslovakia. Alexander Dubcek, aware that the Soviet forces could be used to bring an end to Prague Spring, declined the offer.
On 21st August, 1968, Czechoslovakia was invaded by members of the Warsaw Pact countries. In order to avoid bloodshed, the Czech government ordered its armed forces not to resist the invasion. Alexander Dubcek was taken to Moscow and the reform program in Czechoslovakia was abandoned.
Source:
http://www.spartacus.schoolnet.co.uk/COLDprague.htm