How does a nation know that it's entering a new era? I've recently encountered a promising clue: the sense that the political shibboleths of modern memory—World War II and the Cold War, the great events that have defined the human struggle in our time—are losing their significance to us. We don't revert to them reflexively today, as lynchpins of our reality. We may allude to them as ready sources of historical example, but they no longer wield over our "tribal consciousness" the power that they once did.

This is more than a matter of the passage of time: we are losing a basic definition of ourselves in relation to past and future as well as to good and evil. Through the great 20th-century events, we built up a cultural narrative that framed our destiny in the context of a mighty moral conflict. Our vision of ourselves was shaped by the need to fight against the armed, predatory forms of totalitarianism abroad in the earth. We in the West were the free peoples, and we had a set of touchstones in common: a short list of freedoms, a Judeo-Christian philosophy, and memories of World War II and Korea, of the Berlin Wall and the "Eastern Bloc," of Churchill, Stalin, Mao, Truman, de Gaulle, of John F. Kennedy and the Cuban missile crisis, of Vietnam, the "Prague Spring" of 1968, Margaret Thatcher, Lech Walesa, Ronald Reagan.

Even the prophecy teachers of the time found enduring significance in our cultural touchstones. I remember prophetic meditations in the 1970s on the "eagle" (the United States) and the "bear" (the Soviet Union). It was generally accepted that the Soviet Union would be a participant in the "end times," and widely supposed that Communism was a herald of the Beast described in Revelation 13. The reemergence of the nation of Israel invested everything in the last century with a prophetic significance.

But this era of a common narrative about freedom, totalitarianism, good, and evil seems now to be fading into the past. I was forcibly struck by this a few weeks ago when I saw the new film of John le Carré's 1974 spy novel Tinker, Tailor, Soldier, Spy. Gary Oldman heads an exceptional cast, and the film is nicely crafted and faithful to the le Carré narrative, but I was surprised at the story's lack of resonance on screen. When Western society was in the grip of the Cold War, le Carré's fictional shadow-world was recognizable to all, without explanation or excuse. Today it looks antique, off-kilter, and even rather pointless.

In the last several weeks, I have also been catching episodes of the 1970s-era TV show The Waltons. The series aired from 1972 to 1981, and the later episodes include numerous plots drawn from World War II. In the 1970s, World War II loomed incontestably as the defining event of the century, and for many in the TV audience, seeing the Walton family gathered around the radio listening to news of Pearl Harbor and the Normandy invasion did more than bring back memories. It affirmed the reassuring narrative of the most important triumph in our time of good over evil.

Today, however, while our evaluation of the good-versus-evil aspect is unchanged, the memory of World War II is no longer an immediate and reassuring touchstone. It has receded into a perfunctory data point from the past. So when I saw the movie Casablanca on TV last week, for the first time in several years, I was not surprised to observe that one of the film's most cherished scenes seemed to fall flat.