At approximately 11 pm on 20 August 1968, Eastern Bloc armies from four Warsaw Pact countries – the Soviet Union, Bulgaria, Poland and Hungary – invaded Czechoslovakia.
That night, 250,000 Warsaw Pact troops and 2,000 tanks entered the country.
The total number of invading troops eventually reached 500,000.
Brezhnev was determined to give the operation a multilateral appearance (unlike during the Hungarian Revolution of 1956), but the invasion was dominated by Soviet forces, which outnumbered other troops participating in it roughly five times over.
The invading armies were under the direct control of the Soviet High Command at all times.
Among them were 28,000 soldiers of the Polish 2nd Army from the Silesian Military District, commanded by general Florian Siwicki.
All invading Hungarian troops were withdrawn by 31 October.

Romania did not take part in the invasion, nor did Albania, which subsequently withdrew from the Warsaw Pact over the matter the following month.
The participation of the German Democratic Republic was cancelled just hours before the invasion.
The decision for the non-participation of the East German Army in the invasion was made on short notice by Brezhnev at the request of high-ranking Czechoslovak opponents of Dubček who feared much larger Czechoslovak resistance if German troops were present on Czechoslovak territory, due to previous Czech experience with the German occupation of Czechoslovakia.

The invasion was well planned and coordinated; simultaneously with the border crossing by ground forces, a Soviet airborne division (VDV) captured Ruzyne International Airport) in the early hours of the invasion.
It began with a special flight from Moscow which carried more than 100 plain clothes agents.
They quickly secured the airport and prepared the way for the huge forthcoming airlift, in which An-12 transport aircraft began arriving and unloading VDV equipped with artillery and light tanks.

As the operation at the airport continued, columns of tanks and motorized rifle troops headed toward Prague and other major centers, meeting no resistance.
Despite the fact that the Czechoslovak People's Army was one of the most advanced militaries in Eastern Europe, it did not resist the invasion due to its lack of a chain of command and the government's fears that it would side with the invaders as the Hungarian People's Army did during the Hungarian Revolution in 1956.

During the attack of the Warsaw Pact armies, 137 Czechs and Slovaks were killed, and hundreds were wounded.
Alexander Dubček called upon his people not to resist.
The Central Committee, including Dubček, hunkered down at its headquarters as Soviet forces sezied control of Prague.
Eventually, paratroopers cut the building's telephone lines and stormed the building.
Dubček was promptly arrested by the KGB and taken to Moscow along with several of his colleagues.
Dubček and most of the reformers were returned to Prague on 27 August, and Dubček retained his post as the party's first secretary until he was forced to resign in April 1969 following the Czechoslovak Hockey Riots.

The invasion was followed by a wave of emigration, largely of highly qualified people, unseen before and stopped shortly after (estimate: 70,000 immediately, 300,000 in total).
Western countries allowed these people to immigrate without complications.
At approximately 11 pm on 20 August 1968, Eastern Bloc armies from four Warsaw Pact countries – the Soviet Union, Bulgaria, Poland and Hungary – invaded Czechoslovakia. That night, 250,000 Warsaw Pact troops and 2,000 tanks entered the country. The total number of invading troops eventually reached 500,000. Brezhnev was determined to give the operation a multilateral appearance (unlike during the Hungarian Revolution of 1956), but the invasion was dominated by Soviet forces, which outnumbered other troops participating in it roughly five times over. The invading armies were under the direct control of the Soviet High Command at all times. Among them were 28,000 soldiers of the Polish 2nd Army from the Silesian Military District, commanded by general Florian Siwicki. All invading Hungarian troops were withdrawn by 31 October.
Romania did not take part in the invasion, nor did Albania, which subsequently withdrew from the Warsaw Pact over the matter the following month. The participation of the German Democratic Republic was cancelled just hours before the invasion. The decision for the non-participation of the East German Army in the invasion was made on short notice by Brezhnev at the request of high-ranking Czechoslovak opponents of Dubček who feared much larger Czechoslovak resistance if German troops were present on Czechoslovak territory, due to previous Czech experience with the German occupation of Czechoslovakia.
The invasion was well planned and coordinated; simultaneously with the border crossing by ground forces, a Soviet airborne division (VDV) captured Ruzyne International Airport) in the early hours of the invasion. It began with a special flight from Moscow which carried more than 100 plain clothes agents. They quickly secured the airport and prepared the way for the huge forthcoming airlift, in which An-12 transport aircraft began arriving and unloading VDV equipped with artillery and light tanks.
As the operation at the airport continued, columns of tanks and motorized rifle troops headed toward Prague and other major centers, meeting no resistance. Despite the fact that the Czechoslovak People's Army was one of the most advanced militaries in Eastern Europe, it did not resist the invasion due to its lack of a chain of command and the government's fears that it would side with the invaders as the Hungarian People's Army did during the Hungarian Revolution in 1956.
During the attack of the Warsaw Pact armies, 137 Czechs and Slovaks were killed, and hundreds were wounded. Alexander Dubček called upon his people not to resist. The Central Committee, including Dubček, hunkered down at its headquarters as Soviet forces sezied control of Prague. Eventually, paratroopers cut the building's telephone lines and stormed the building. Dubček was promptly arrested by the KGB and taken to Moscow along with several of his colleagues. Dubček and most of the reformers were returned to Prague on 27 August, and Dubček retained his post as the party's first secretary until he was forced to resign in April 1969 following the Czechoslovak Hockey Riots.
The invasion was followed by a wave of emigration, largely of highly qualified people, unseen before and stopped shortly after (estimate: 70,000 immediately, 300,000 in total). Western countries allowed these people to immigrate without complications.
Warsaw Pact invasion of Czechoslovakia