I own a piece of the Wall. One of my most prized possessions is the undistinguished chunk of concrete that a journalist friend brought back for me after watching East and West German students and citizens pulverize, stone by stone, the century’s most enduring symbol of tyranny. The piece of gray rubble occupies a place of honor on my desk.

The 20th anniversary of the beginning of the end of Communism has, of course, prompted an outpouring of scholarly books, adding to the already vast literature on what Francis Fukuyama would unfortunately call the “end of history.” (His provocative, original book had perhaps the world’s most misleading title.) Despite the scholars’ work, however, much about the causes and social dynamics of the popular uprisings that triggered Communism’s collapse remains elusive, as Timothy Garton Ash recently wrote in The New York Review of Books. Ash spent many thrilling hours among the ecstatic crowds of Warsaw, Budapest, Berlin, and Prague, chronicling the protesters’ hopes, doubts, and fears. But even two decades later, he writes, what “moved these men and women to come out on the streets, especially in the early days, when it was not self-evidently safe to do so” remains both inspiring and profoundly mysterious.

Partly for that reason, it’s easy to forget how momentous an event the wall’s collapse was. While it was not an American victory, the wall’s demise owed much to American containment policy and to the president whom so many intellectuals love to hate: Ronald Reagan, who in 1987 dared Mikhail Gorbachev to “tear down this wall,” foreshadowing its collapse by only two years. The appeal of those words still resounds, oddly overshadowing his prediction at the end of the same speech: “This wall will fall,” he asserted. “For it cannot withstand faith; it cannot withstand truth. The wall cannot withstand freedom.” Reagan, a deeply underestimated president, called out the Communist system for what it was: an evil empire. Both he and his successor were wise enough not to interfere with its collapse.

The mass protests and political upheavals in Europe are especially impressive if we recall that 1989 is also the 20th anniversary of the Tiananmen Square massacre, which, Ash reminds us, occurred “on the very day of Poland’s breakthrough in a semifree election.” China, of course, was willing to do what East German and Russian rulers were not—shoot the protesters in mass numbers. After the events of 1989, the Chinese Communist Party carefully studied the lessons of the collapse of Communism in Europe, Ash writes, “to make sure it did not happen to them.” Today’s China, he concludes grimly, “is a result of that learning process.”

Two years after the Soviet Union’s dissolution, I was touring some of the germ-weapons labs and giant production facilities that were scattered through the former empire. Moscow had violated the treaty banning such weapons before the ink on the signature line had dried. Tens of thousands of Soviet citizens had lived in secret cities—behind high electrified walls—dedicated to the illicit creation and production of ever more lethal bacteria and viruses. The only word that came to mind to describe what I was seeing was “evil.”

But neither history nor evil ended with the disappearance of the wall or the Soviet Union. Communism has been relegated, appropriately, to the junkyard of discredited political movements—though China, North Korea, and a few others continue paying it lip service—but the world confronts new forms of evil. Militant Islamists, who pervert a great faith and practice repression and violence with godly faces, do not yet control a powerful, nuclearized state as the Communists did. But they do rule Iran, Sudan, and Gaza, and they vie for power in half a dozen Arab Muslim states. They, too, demand “submission,” this time in the name of God. They, too, are building walls—around their covert nuclear facilities, between the sexes, and to separate the anointed from the “infidels” who live in sin and ignorance. Israel has responded with its own wall, this one built to keep extremists out and its own population safe.

Militant Islam’s banner is green, not red, but its triumph would usher in a new era of intolerance and another civilizational struggle. Twenty years after the wall came down, the West has more history to make.

Judith Miller is a contributing editor of City Journal where this piece first appeared. She is an adjunct fellow at the Manhattan Institute and a FOX News contributor.

Judith Miller, a Fox News contributor, is an award-winning writer and author, and an adjunct fellow at the Manhattan Institute. The author of several books, her latest is "The Story: A Reporter's Journey" (Simon & Schuster, April 7, 2015) now available in paperback. Follow her on Twitter @JMFreeSpeech.