THIRTY YEARS AGO, on June 8, 1982, President Reagan delivered an address to the British Parliament that stands as one of the greatest of his presidency and a milestone in the final years of the Cold War. At a time when the Soviet Union seemed to be a permanent, if foreboding, presence in the world, Reagan predicted that “the march of freedom and democracy” would “leave Marxism-Leninism on the ash heap of history as it has left other tyrannies which stifle the freedom and muzzle the self-expression of the people.”

The “ash heap of history” was language Mr. Reagan personally wrote into the address, according to Robert C. Rowland and John M. Jones, who wrote a book about the making of the speech, “Reagan at Westminster: Foreshadowing the End of the Cold War.” The words reflected Mr. Reagan’s notion, not universally accepted at the time, that the West should not just criticize or contain Soviet behavior but also challenge the basic legitimacy of the Soviet system.

“I believe we now live at a turning point,” Mr. Reagan declared in the speech at Westminster Palace. “In an ironic sense, Karl Marx was right. We are witnessing today a great revolutionary crisis.” But the crisis was not in the West, Mr. Reagan asserted. Rather it was unfolding in “the home of Marxist-Leninism, the Soviet Union. It is the Soviet Union that runs against the tide of history by denying human freedom and human dignity to its citizens.” He went on to offer trenchant insights into the Soviet Union as a dysfunctional, doomed experiment, a vast land that could not even feed itself. “Overcentralized, with little or no incentives, year after year the Soviet system pours its best resource into the making of instruments of destruction,” he said.

In the first years of his presidency, Mr. Reagan was brimming with this kind of ideological confrontation, which reached a peak in 1983 when he called the Soviet Union an “evil empire.” But three Soviet leaders died in succession, Mr. Reagan underwent his own metamorphosis and he eventually found in Mikhail Gorbachev someone he could do business with. In the Westminster speech, Mr. Reagan had presciently grasped the real and deepening crisis of communism. When the Soviet Union did finally implode in 1991, the fissures Mr. Reagan had described a decade before were the cause.

Mr. Reagan pledged in the Westminster speech to boost support for democracy around the globe, and a year after his speech, Congress created the National Endowment for Democracy. Although Mr. Reagan’s focus was on the Soviet bloc, his vision has endured long after Soviet communism expired. The National Endowment for Democracy is active in more than 90 countries.

Recent events in China, Russia and the Arab world vividly demonstrate that democracy remains a universal aspiration — but also that the forces of repression have powerful means to resist the tide. The National Endowment for Democracy, and like-minded agencies that other democracies subsequently established, have found useful ways to aid and nurture freedom movements. Words, too, are important. Reading the Westminster speech is a good reminder of their power to inspire action, and change history.