Understanding the Prague Spring
On January 5, 1968, Alexander Dubček came to power in Communist Czechoslovakia, and began a series of reforms, later called the "Prague Spring." His new policies centered around the idea that Communism could be more liberal and responsive to the people, and achieved by increasing freedom of the press, emphasizing consumer goods, and the suggesting a multi-party government instead of a Communist dictatorship. On August 21, 1968, the Soviet Union and its Warsaw Pact allies invaded Czechoslovakia to end the liberal policies of the Dubček government. The following excerpt is from a CIA intelligence report, which laid out the basic causes of Dubček's rise to power, and discussed why the Warsaw Pact could effectively stop him. Though the Prague Spring of 1968 was a short-lived reaction against the Warsaw Pact, many of these preconditions for revolution against Communism would emerge again in the 1980s, especially following the Soviet disarmament policies in Eastern Europe.
Central Intelligence Agency, "Czechoslovakia: The Problem of Soviet Control," 16 January 1970, CIA CIA Library (accessed June 27, 2007).
The story of Czechoslovakia in 1968 can be told from many perspectives ... This report concentrates on the loss and restoration of Soviet control. The Soviet Union's extensive political influence over neighbors with a common ideology cannot be ignored, but this report emphasizes political control in the specific and concrete sense, and the military and political prerequisites for it.
For almost 20 years, Czechoslovakia was a model satellite. However, increasingly dangerous anomalies had begun to weaken Soviet control ... When liberals and Slovaks combined to elect Dubcek party first secretary in January 1968 ... [h]e turned for support to the liberals who were then formulating and advocating popular reform programs. Finding support among the liberals and from the populace, he began to bypass mechanisms of Soviet control and instituted reforms which further threatened the prerequisites for Soviet control.
At the end of March 1968, apparently in response to East German and Polish alarm, the Soviet and Bloc leaders (minus Romania) met to caution the Czechoslovaks on their reforms. ... A final Soviet effort to coerce or split the Czechoslovak party and leadership and to recruit pro-Soviet leaders among them was made at Cierna at the end of July. ... The events of the first weeks of August  proved that the Czechoslovak leaders would not or could not live up to the Soviet demands put on record at the Bratislava meeting of Bloc leaders (minus Romania) immediately after the Cierna meeting. On the night of 20-21 August 1968, the Warsaw Pact forces which had been building up on the borders for months swiftly and efficiently occupied the country.
The restoration of full party control, and through the party, of Soviet control, was increasingly swift and ruthless [during the following months]. By mid-May  the mass media had been brought under conservative control by replacement of all key personnel. By the beginning of June liberals had been purged from the party organizations of Bohemia and Moravia. In July and August the history of the previous year was rewritten to transfer the taint of "treason" at the time of the invasion from the conservatives to the liberals. Those who demonstrated against the Soviets on the anniversary of the invasion were beaten by Czechoslovak security forces while Soviet forces remained out of sight.