THE LINE DIVIDING MEMORY FROM HISTORY is a thin one. The latter hinges on reportage, reconstruction, and, inevitably, speculation; the former is personal, immediate and in some cases dramatic. It is twenty years since the collapse of the Soviet Union, but my memories of it are sharp. Waking up in Moscow to the news of the August 1991 military coup against the reforming Soviet president Mikhail Gorbachev; driving down Gorky Street as columns of tanks descended on the Kremlin, sent by the disgruntled hardline communists who claimed to have seized power; talking to the tank crews and hearing from nervous conscripts that they had live ammunition in their weapons and were prepared to use it. For three anxious days the fate of Europe and the world was fought over on the streets of Moscow.

After nearly a decade of reporting from the Soviet Union, I had known for some time that Gorbachev’s perestroika was in trouble. His liberalizing reforms hadn’t delivered the goods, either politically or in the nation’s food stores. Earlier in the year Kremlin hardliners had surreptitiously fomented unrest in the Baltic republics; now they were going for broke.

Their template for seizing power seemed to be the October 1964 ousting of the reformist Nikita Khrushchev by the Brezhnev clique. Both then and in 1991, the coup plotters had made their move while the leader was absent from Moscow. Both had secured, or attempted to secure, the backing of the power ministries — army, interior, security services — knowing they would be decisive in the event of a struggle. And both had grabbed the levers of centralized power. The Soviet Communist Party’s so-called democratic centralism, its web of administrative domination radiating from the Kremlin, ensured that commands from the top resulted in obedience on the ground. But there were differences between 1964 and 1991 that would emerge as the coup progressed.

When I spoke to Muscovites on the streets, I found some who agreed with the coup leaders, attracted by their promises to revive the economy, end the shortages, and re-establish the USSR as a superpower. But there was defiance, too, with civilians haranguing the troops or standing in the way of the tanks.

I watched as a detachment of armored vehicles encircled the Russian Parliament building, belching acrid smoke, churning up the blacktop of the Moskva River embankment. I saw Muscovites shot and crushed to death by armored personnel carriers. And I witnessed the crucial moment of political theatre when Boris Yeltsin clambered onto the back of a tank to urge the Russian people to unite against the coup.

The big change since 1964 was that the Russian people were no longer resigned to the ineluctability of a political process played out by shadowy cliques in the Kremlin. Khrushchev’s reforms were carried out within the rules of the system, so the system, with absolute power concentrated in the hands of the Party’s ruling elite, could...