On the night of August 20 - August 21, 1968, the Soviet Union and four of its Warsaw Pact allies invaded the Czechoslovak Socialist Republic in order to halt Alexander Dubček's Prague Spring political liberalization reforms.
In the operation, codenamed Danube, varying estimates of between 175,000 and 500,000 troops attacked Czechoslovakia; 108 Czechoslovaks died and approximately 500 were wounded as a direct result of the invasion. The invasion successfully stopped liberalization reforms and strengthened the authority of the Communist Party of Czechoslovakia.
The foreign policy of the Soviet Union during this era would be known as the Brezhnev Doctrine.
On August 3, representatives from the Soviet Union, East Germany, Poland, Hungary, Bulgaria, and Czechoslovakia met in Bratislava and signed the Bratislava Declaration. The declaration affirmed unshakable fidelity to Marxism-Leninism and proletarian internationalism and declared an implacable struggle against "bourgeois" ideology and all "antisocialist" forces. The Soviet Union expressed its intention to intervene in a Warsaw Pact country if a "bourgeois" system—a pluralist system of several political parties representing different factions of the capitalist class—was ever established. After the Bratislava conference, Soviet troops left Czechoslovak territory but remained along Czechoslovak borders.
As these talks proved unsatisfactory, the Soviets began to consider a military alternative. The Soviet Union's policy of compelling the socialist governments of its satellite states to subordinate their national interests to those of the "Eastern Bloc" (through military force if needed) became known as the Brezhnev Doctrine.
At approximately 11 pm on August 20, 1968, Eastern Bloc armies from five Warsaw Pact countries, Soviet Union, Bulgaria, Poland, Hungary, and East Germany, invaded the ČSSR. That night, 200,000 Warsaw Pact troops and 2,000 tanks entered the country. Among them were 28,000 troops of Polish 2nd Army from Silesian Military District, commanded by general Florian Siwicki. The Hungarian troops were withdrawn by October 31. Romanian troops did not take part in the invasion, and neither did Albania, which withdrew from the pact over the matter. The degree of participation of East German troops is doubtful, either they were withdrawn within a few days or barely crossed the border. During the attack of the Warsaw Pact armies, 72 Czechs and Slovaks were killed (19 of those in Slovakia) and hundreds were wounded. Alexander Dubček called upon his people not to resist. He was arrested and taken to Moscow along with several of his colleagues. Dubček and most of the reformers were returned to Prague on August 27, 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, unseen before and stopped shortly after (estimate: 70,000 immediately, 300,000 in total), typically of highly qualified people. Western countries allowed these people to immigrate without complications.
Although on the night of the invasion, the Czechoslovak Presidium declared that Warsaw Pact troops had crossed the border without knowledge of the ČSSR Government, the Soviet Press printed an unsigned request, allegedly by Czechoslovak party and state leaders, for "immediate assistance, including assistance with armed forces." At the 14th KSČ Party Congress (conducted secretly, immediately following the intervention), it was emphasized that no member of the leadership had invited the intervention. At the time, a number of commentators believed the letter was fake or non-existent.
In the early 1990s, however, the Russian government gave the new Czechoslovak President, Václav Havel, a copy of a letter of invitation addressed to Soviet authorities and signed by KSČ members Biľak, Švestka, Kolder, Indra, and Kapek. It claimed that “right-wing” media were “fomenting a wave of nationalism and chauvinism, and are provoking an anti-communist and anti-Soviet psychosis.” It formally asked the Soviets to “lend support and assistance with all means at your disposal” to save the Czechoslovak Socialist Republic “from the imminent danger of counterrevolution.” A 1992 Izvestia article claimed that candidate Presidium member Antonin Kapek gave Leonid Brezhnev a letter at the Soviet-Czechoslovak Čierna nad Tisou talks in late July which appealed for “fraternal help.” A second letter was supposedly delivered by Biľak to Ukrainian Party leader Petro Shelest during the August Bratislava conference “in a lavatory rendezvous arranged through the KGB station chief.” This letter was signed by the same five as Kapek’s letter, mentioned above.
Long before the invasion, planning for a coup was undertaken by Indra, Kolder and Biľak, among others, often at the Soviet embassy and at the Party recreation centre at Orlík Dam. When these men had managed to convince a majority of the Presidium (six of eleven voting members) to side with them against Alexander Dubček’s reformists, they asked the Soviets to launch a military invasion. The Soviets were even considering waiting until the August 26 Slovak Party Congress, but the Czechoslovak conspirators “specifically requested the night of the 20th.” The plan was to unfold as follows. A debate would unfold in response to the Kašpar report on the state of the country, during which conservative members would insist that Dubček present two letters he had received from the Soviets, letters which listed promises he had made at the Čierná nad Tisou talks but had failed to keep. Dubček’s concealment of such important letters, and his unwillingness to keep his promises would lead to a vote of confidence which the now conservative majority would win, seizing power, and issue a request for Soviet assistance in preventing a counterrevolution. It was this formal request, drafted in Moscow, which was published in Pravda on August 22 without the signatories. All the Soviets needed to do was suppress the Czechoslovak military and any violent resistance. With this plan in mind, the August 16-17 Soviet Politburo meeting passed a resolution to “provide help to the Communist Party and people of Czechoslovakia through military force.” At the August 18 Warsaw Pact meeting, Brezhnev announced that the intervention would go ahead on the night of August 20, and asked for "fraternal support", which the national leaders of Bulgaria, East Germany, Hungary, and Poland duly offered.
The conservatives asked Svoboda to create an "emergency government" but since they had not won a clear majority of support, he refused. Instead, he and Gustáv Husák traveled to Moscow on August 23 to insist Dubček and Černík should be included in a solution to the conflict. After days of negotiations, the Czechoslovak delegation accepted the "Moscow Protocol", and signed their commitment to its fifteen points. The Protocol demanded the suppression of opposition groups, the full reinstatement of censorship, and the dismissal of specific reformist officials. It did not, however, refer to the situation in the ČSSR as "counterrevolutionary" nor did it demand a reveral of the post-January course.
Popular opposition was expressed in numerous spontaneous acts of nonviolent resistance. In Prague and other cities throughout the republic, Czechs and Slovaks greeted Warsaw Pact soldiers with arguments and reproaches. Every form of assistance, including the provision of food and water, was denied the invaders. Signs, placards, and graffiti drawn on walls and pavements denounced the invaders, the Soviet leaders, and suspected collaborators. Pictures of Dubček and Svoboda appeared in the streets.
Initially, some civilians tried to argue with the invading troops, but this met with little or no success. After the Soviets used photographs of these discussions as proof that the invasion troops were being greeted amicably, secret Czechoslovak broadcasting stations discouraged the practice, reminding the people that "pictures are silent.
The generalized resistance caused the Soviet Union to abandon its original plan to oust the First Secretary. Dubček, who had been arrested on the night of August 20, was taken to Moscow for negotiations. It was agreed that Dubček would remain in office and that a program of moderate reform would continue.
Finally, on April 17, 1969, Dubček was replaced as First Secretary by Gustáv Husák, and a period of "Normalization" began. Husák reversed Dubček's reforms, purged the party of its liberal members and dismissed the professional and intellectual elites who openly expressed disagreement with the political turnaround from public offices and jobs.
Many people in the Soviet Union did not approve of the invasion. On August 25, on the Red Square, 8 protesters opened banners with anti-invasion slogans. The demonstrators were arrested and later punished; as the protest was dubbed "anti-Soviet".
In the German Democratic Republic, the invasion aroused a fair share of discontent among those who had hoped that Czechoslovakia would pave the way for a more liberal socialism. However, isolated protests were quickly stopped by the police and stasi.
In the People's Republic of Poland, on 8 September 1968, Ryszard Siwiec had immolated himself in Warsaw during a harvest festival at the 10th-Anniversary Stadium in protest against Warsaw Pact invasion of Czechoslovakia and the communist totalitarianism. Severely burned, Siwiec was transferred to the hospital where he died.
The night of the invasion, Canada, Denmark, France, Paraguay, the United Kingdom and the United States all requested a meeting of the United Nations Security Council. That afternoon, the council met to hear the Czechoslovak Ambassador Jan Muzik denounce the invasion. Soviet Ambassador Jacob Malik insisted the Warsaw Pact actions were "fraternal assistance" against "antisocial forces." The next day, several countries suggested a resolution condemning the intervention and calling for immediate withdrawal. US Ambassador George Ball, suggested that "the kind of fraternal assistance that the Soviet Union is according to Czechoslovakia is exactly the same kind that Cain gave to Abel." Ball accused Soviet delegates of filibustering to put off the vote until the occupation was complete. Malik continued to speak, ranging in topics from US exploitation of Latin America's raw materials to statistics on Czech commodity trading. Eventually, a vote was taken. Ten members supported the motion; Algeria, India, and Pakistan abstained; the USSR (with veto power) and Hungary opposed it. Canadian delegates immediate introduced another motion asking for a UN representative to travel to Prague and work for the release of the imprisoned Czechoslovak leaders. Malik accused Western countries of hypocrisy, asking "who drowned the fields, villages and cities of Viet-Nam in blood?" By August 26, another vote had not taken place, but a new Czechoslovak representative requested the whole issue be removed from the Security Council's agenda.
Although the United States insisted at the UN that Warsaw Pact aggression was unjustifiable, its position was compromised by its own actions. Only three years earlier, US delegates to the UN has insisted that the overthrow of a leftist government Dominican Republic as part of Operation Power Pack was an issue to be worked out by the Organization of American States (OAS) without UN interference. The OAS accepted adherence to Marxism-Leninism as an armed attack justifying self-defense by the United States. American involvement in the Vietnam War led UN Secretary-General U Thant to draw further comparisons, suggesting that "if Russians were bombing and napalming the villages of Czechoslovakia" he might be more vocal in his denunciation.
In effect, the western countries offered only vocal criticism following the invasion — the reality of the Cold War meant they were in no position to challenge Soviet military force in Central Europe, without risking nuclear war.
A more pronounced effect took place in Communist Romania, where leader Nicolae Ceauşescu, already a staunch opponent of Soviet influences and one to have declared himself on Dubček's side, held a public speech in Bucharest on the day of the invasion, depicting Soviet policies in harsh terms. While Romania engaged briefly on the same side of the barricade as Josip Broz Tito's Yugoslavia, the alliance was purely conjectural (as Ceauşescu was already proved to be opposed to the principle of a Socialism with a human face). It did however consolidate Romania's independent voice in the next decades, especially after Ceauşescu encouraged the population to take up arms in order to meet any similar maneuver in that country: he received an enthusiastic initial response, with many people who were by no means communist willing to enroll in the newly-formed paramilitary Patriotic Guards.
In Finland, a neutral country under some Soviet political influence at that time, the occupation caused a major scandal. Like the Italian and French Communist Parties, the Communist Party of Finland denounced the occupation. Nonetheless, Finnish president Urho Kekkonen was the very first Western politician to officially visit Czechoslovakia after August 1968; he received the highest Czechoslovakian honours from the hands of president Ludvík Svoboda, on October 4, 1969.
The Portuguese communist secretary-general Álvaro Cunhal is believed to have been the only political leader from western Europe to have supported the invasion for being counterrevolutionary, along with the Luxembourgian Communist Party.
The United States government sent Shirley Temple Black, the famous child movie star, who became a diplomat in later life, to Prague in August 1968 to prepare to become the first United States Ambassador to free Czechoslovakia. Two decades later, when Czechoslovakia became independent, Mrs. Black was the first United States ambassador to the country.
Countries of Eastern Europe begun to seek protection in NATO.
The suppression of the Prague spring is used as precedent in analysis of military conflicts in XXI century.