That was 43 years ago. I know because I was born almost at the same time. The night between the 20th and 21st of August of 1968 an imperialist coup by the USSR took place in Czechoslovakia, by means of arresting its reformist Premier Alexander Dubček and then invading the binational Carpathian state.
This way possible reform from inside of the authoritarian excesses of Real Socialism in Europe was thwarted for the second time, making unavoidable the degeneration that would come in the 1970s and 80s and the eventual collapse of all Socialism in Europe (and much of the rest of the World, because what exists in China or Vietnam is not Socialism anymore, except maybe in the twisted fascist or socialdemocratic usage of the term: socialism as mere auxiliary state intervention in favor of Capitalist accumulation and exploitation).
The roots: a too shy de-Stalinization
A good deal of the problems that plagued socialist revolutions in the 20th century were caused by the reactionary, yet still partly revolutionary, takeover by Stalin in the 1920s. Ioseb Besarionis dze Jughashvili, best known by the Russified form of his surname: Stalin, was maybe the most important single individual of the 20th century, not necessarily for the right reasons. He probably got his mentor Lenin killed and took power even before his death.
Like those pseudo-cooperative ant queens that join forces early in the hope of being them the only one eventually surviving, Stalin lead the Soviet conspirators against each other once and again, managing to stay on top until his death. Of a quite darker but also less militarist shade, Stalin can be compared (and punctually also contrasted) with Napoleon Bonaparte. The same that Napoleon I led the reaction within the French Revolution (but was never really accepted by the International old regime led by Britain), Stalin led the reaction within the Russian Revolution and he was also only never really accepted by the hegemons of the age: Britain first and then its heir: the USA.
Because of Nazi imperialism, Stalin ended up his days with a quite sizable "revolutionary empire" of sorts, controlling half Europe and wielding widespread influence in Asia, Africa and even America. Much of this "empire" however owed at least partly to the struggles of peoples who willingly put themselves under Moscow's protection. That was the case of Albania, Vietnam, Cuba... and that was also the case of Czechoslovakia.
However, Stalin was an clear excess and his heirs took no time in proclaiming the De-Stalinization, throwing down most of the statues of the Batyushka and vigorously denouncing the purges and the cult of personality. However all this was little more than a make up, with no real deep changes, very much needed. In fact the period initiated by Beria and Krushev is sometimes described as Neo-Stalinism or Stalinism without Stalin.
In the particular case of Czechoslovakia, De-Stalinization arrived late and very weakly. While nearby Hungary was shattered by a revolution in 1956, Czechoslovakian communists were still extending the life span of classical Stalinism almost artificially and purging dissidents with this doctrine.
The 1960s reforms
But this conservatism caused stagnation and led to unavoidable reforms in the vigorous 1960s. In 1965 there was a full fledged revision of the concept of democratic centralism, the emphasis was now in democracy and the end date for its implementation was 1967. When the day of truth came however, the authorities hesitated, specially as Slovak separatism and pro-Western and pro-market opinions grew in strength. No wonder.
However, the Kremlin was even willing to accept market-oriented reforms, what was not willing to allow was genuine democracy, where different options would be available for the people to choose. This discursive confusion of formal democracy with Capitalism is totally made up by Stalinism (and successors). While the Capitalist democratic farce was often denounced by Socialists and Communists for being highly imperfect and not allowing economic democracy (the economy remains in the private hands of the oligarchy in the Bourgeois systems no matter how many lists and candidates stand in elections or how many people can vote) and described as Dictatorship of the Bourgeoisie, the pretense that mere nationalization of industries and waving a red banner was enough to make a true People's Power, a true Democracy, is clearly false. At best the party dictatorship can be considered as a transitional stage, at worst as grand treason.
Initially Khrushchev let the Czechoslovaks decide their path freely however, fear among other late Stalinist rulers in East Germany and Poland, inside the USSR itself and in the most reactionary sectors of the Czechoslovak Communist Party (KSČ) seems to have leaned the scales towards a coup accompanied by military intervention.
Secretly, six members out of eleven of the Politburo wrote an appeal to Moscow for intervention, which would happen jointly with an internal coup. The coup would take place on August 20th but, in the last minute, notice of the invasion arrived from Hungary and the Politburo voted on it, with most, including two of the conspirators opposing it. This and the fact that the reforms were massively popular in the Central European republic, left the Warsaw Pact invasion without any internal support.
While there was widespread, mostly nonviolent, resistance, there was little that Czechoslovaks could do in the short term against such a mighty army. Dubček and other reformists were flown to Moscow but later had to be included in a compromise because the conservatives had so little support that they could not act on their own.
Yet a few months later Dubček was replaced by Huśak, who essentially revoked all his predecessor's reforms.
Romania did not take part in the invasion and used it to reinforce its nationalist (but not liberal, Ceaucescu was a good friend of General Franco, go figure!) autonomy from Moscow, Albania (which was the only red state that remained 100% Stalinist until the 1990s) used it as pretext to exit the organization. There were also lesser protests in Warsaw (where Ryszard Siwiec set himself on fire), Moscow and East Germany.
That night, the hope for a democratic real socialism and for a socialist true democracy waned under the military boot. Since then all has been Stalinist decadence and Reaganist despair... all my life, to the minute almost. Time for the tide to change.