Russia’s invasion of Georgia comes 40 years after another Kremlin act of aggression against a small, nearby, and independent-minded country.

Czechoslovakia was the victim in that earlier instance. A communist country and a vassal state of the Soviet empire, Czechoslovakia’s party leadership had initiated a reform process, dubbed the Prague Spring, that sought to infuse state socialism with elements of civil liberties and the market. It was the first attempt to “reform” communism from inside party ranks. The party leader, Alexander Dubcek, and his allies intended to move carefully — as communists they recognized the dangers in a reform movement that the party was unable to manage.

Yet in a process that would be repeated, with profound consequences, two decades later in the Soviet Union of Mikhail Gorbachev, reform took on a life of its own. Freed from the mental straightjacket of Marxist ideology, the more daring reformers began to press for far-reaching change and to ask forbidden questions. Something approximating a free press emerged, and journalists began poking around in the many dark corners of the communist past.

The Soviet leadership summoned Dubcek, pounded the table, and issued threats. When these were ignored, a massive military force was dispatched, ostensibly at the request of unnamed Czechs and Slovaks, to quell “counterrevolution.” After a quisling leadership was imposed, normalcy was said to reign, and there was no talk of reform for the next 21 years, until communism collapsed throughout Eastern Europe.

One must resist the temptation to draw facile comparisons between the Prague Spring of 1968 and today’s conditions in Russia and its environs. After all, communism is defunct, and, as we have been repeatedly reminded, a Cold War mindset is inappropriate in the 21st century. Yet for those who take the time to reflect on the Prague Spring legacy, a few points are worthy of note.

First, the Soviet Union and today’s Russia share a profound hostility to democracy on their borders. While the architects of the Prague Spring denied an abandonment of socialism, the Kremlin understood that the reform trajectory would inevitably lead to democracy, and acted accordingly.

Prime Minister Putin likewise reserves his greatest anger for the democracies on Russia’s periphery. Indeed, Russia maintains generally friendly relations with authoritarian neighbors, including some who are economic rivals. It is the democracies — the Baltics, Ukraine, Poland, Georgia — that have been the objects of intimidations, energy cutoffs, and cyber attacks.

Second, while the Soviets easily succeeded in bringing their errant satellite to heel, they paid a price for intervention. European leftists repudiated the invasion and moved from there to renounce communism itself. Mr. Putin has benefited from a tendency of many Western observers to ignore or rationalize his authoritarian direction. The question is whether his actions in Georgia will trigger second thoughts in his apologists.

Conversely, in a perverse way, aggression in Georgia might strengthen Russia’s hostility toward its democratic neighbors. Here history provides guidance. After the Red Army crushed the Prague Spring, Europe and America concluded that the West should actually reduce the instability inherent in Moscow’s relations with its satellites. The code of subsequent American-Soviet detente was an American acknowledgement that it would refrain from policies that stirred up discontent in Eastern Europe.

Democracy’s response to Georgia will depend on America. In 1968, America was mired in multiple crises that make today’s problems pale in comparison: Vietnam, assassinations, race riots, campus takeovers. The invasion of Czechoslovakia coincided with the Democratic Convention, notable for clashes between anti-war demonstrators and the police. Under these circumstances, Americans hardly noticed events in central Europe; the candidate of the anti-war forces, Eugene McCarthy, flatly refused to condemn the invasion.

America’s response to Georgia has been seemingly clear and strong. But just as Lyndon Johnson ignored unmistakable signs of planned Soviet intervention, so the Bush administration failed utterly to take Moscow to task for its many pre-invasion provocations.

The challenge will be to sustain a bipartisan policy that is anchored on the defense of a beleaguered ally with democratic aspirations and, beyond that, forthright support for Russia’s democratic neighbors. Unfortunately, by failing to act with resolution earlier, the administration approaches this struggle from a position of distinct weakness.

If the Prague Spring represents a dark moment for the West, it stands as an experiment in freedom that is to the enduring credit of its participants. Its peaceful nature set the tone for the later revolutions that brought freedom to Czechs, Slovaks, and other subjugated European peoples.

The crisis in Georgia is a depressing reminder of the fragile nature of those achievements in the face of an emboldened and antidemocratic adversary.

Mr. Puddington is the director of research at Freedom House.