From Postwar: A History of Europe Since 1945, by Tony Judt (Penguin, 2005), pp. 444-447:
On August 21st 1968, 500,000 Warsaw Pact troops from Poland, Hungary, Bulgaria, the DDR and the Soviet Union marched into Czechoslovakia. The invasion met some passive resistance and quite a lot of street protests, especially in Prague; but at the urgent behest of the Czech government it was otherwise unopposed. The unfriendly reception was a source of some surprise to the Soviet leadership, who had been led to expect that their tanks would encounter widespread support. Having at first arrested Dubček and his leading colleagues, flown them to Moscow and obliged them to sign a paper renouncing parts of their program and agreeing to the Soviet occupation of their country, the Kremlin was now perforce obliged to accept that the reformers had the support of the Czech and Slovak people and allow them to retain formal charge of their country, at least for the moment. It was clearly imprudent to do otherwise.
Nevertheless, the repression of the Prague reforms—‘normalization’, as it became known—began almost immediately…. The ‘screening’ and purging of [dissident] intellectuals was carried out by lower ranking bureaucrats, policemen and party officials—more often than not the victims’ own colleagues. Their goal was to extract petty confessions—not so much in order to incriminate their victims but rather to humiliate them and thus secure their collaboration in the self-subjugation of a troublesome society. The message went out that the country had passed through a mass psychosis in 1968, that false prophets had exploited the ensuing ‘hysteria’, and that the nation needed to be directed firmly back to the correct path: induced by the carrot of consumer goods and the stick of omnipresent surveillance.
The threat of violence was of course always implicit, but the fact that it was rarely invoked merely added to the collective humiliation. Once again, as in 1938 and again in 1948, Czechoslovakia was being made complicit in its own defeat. By 1972—with poets and playwrights forced to clean boilers and wash windows; university lecturers stacking bricks, and their more troublesome students expelled; the police files full of useful ‘confessions’; and reform Communists cowed or else in exile—‘order’, in the words of a brilliant, bitter essay by one of normalization’s victims, had been ‘restored’.
There were ripples of protest throughout the Communist bloc…. East European army units engaged in the invasion of Czechoslovakia had been led to believe that they were defending the country against West German or American invaders, and some of them had later to be quietly withdrawn, their reliability—notably that of Hungarian units occupying Slovakia—seriously in question. In Poland, as we have seen, the repression in Prague both stimulated student protests and strengthened the hand of the authorities in stamping them down…. The attitude of Czechs and Slovaks themselves, hitherto among the most pro-Russian nations in the Soviet bloc, now shifted irrevocably to a stance of sullen acquiescence.
But all this was easily contained. The Kremlin had made its point—that fraternal socialist states had only limited sovereignty and that any lapse in the Party’s monopoly of power might trigger military intervention. Unpopularity at home or abroad was a small price to pay for the stability that this would henceforth ensure. After 1968, the security of the Soviet zone was firmly underwritten by a renewed appreciation of Moscow’s willingness to resort to force if necessary. But never again—and this was the true lesson of 1968, first for the Czechs but in due course for everyone else—never again would it be possible to maintain that Communism rested on popular consent, or the legitimacy of a reformed Party, or even the lessons of History….
Reflecting in later years upon his memories of August 21st 1968, when Red Army troops burst into a meeting of Czech party leaders and a soldier lined up behind each Politburo member, [Zdeněk] Mlynář recalled that ‘at such a moment one’s concept of socialism moves to last place. But at the same time you know that it has a direct connection of some sort with the automatic weapon pointing at your back.’ It is that connection which marked the definitive turning point in the history of Communism, more even than the Hungarian tragedy of 1956.
The illusion that Communism was reformable, that Stalinism had been a wrong turning, a mistake that could still be corrected, that the core ideals of democratic pluralism might somehow still be compatible with the structures of Marxist collectivism: that illusion was crushed under the tanks on August 21st 1968 and it never recovered.
One of the 80,000 Czechs and Slovaks who fled into exile following the Soviet invasion was my fellow fieldworker in Papua New Guinea and sometime officemate and housemate during my grad school years.