Always at the heart of America as a moral experiment has been the question of how to make the nation’s power virtuous. Can power ever be virtuous? It’s an almost theological riddle. On D-Day, June 6, 1944, the two—power and virtue—were neatly aligned. Good confronted evil; such clarity gives courage.

The invasion became a bloody, yet treasured, memory of America the Good, a story we have carried over from the olden time—that is, the twentieth century—as a parable of selflessness, in which the dragon of Hitlerism is slain and the continent of Europe is delivered from evil. It was a gesture on the grandest scale, democracy rising to an act of high chivalry—arguably the mightiest feat of arms in the history of the world.

The men who fought at Normandy, 75 years ago, are either gone or in their mid-nineties and older. The national memory relies on movies—The Longest Day or the graphic beginning of Saving Private Ryan—but the courage and sacrifice of the men were real and unforgettable. In this century’s atmosphere of media and political illusion, the decisive reality of D-Day makes us wistful—not for the terrible violence of it, but for the magnificent truth of what was being done and what was at stake.

The nuclear bombing of Hiroshima and Nagasaki, which ended the Second World War 14 months later, represented a different sort of feat entirely. The hero of that story, if there was one, was either the physicist J. Robert Oppenheimer or Harry S. Truman, and neither was proud of what happened. When the 75th anniversary of the nuclear age arrives next summer, those atom bombs—called Fat Man and Little Boy—will not be remembered triumphantly, but instead as a mixed blessing that defeated Japan, and at the same time, opened a new metaphysical abyss. Clarities blurred or vanished. Hiroshima and Nagasaki made D-Day the last great military violence that could be described as virtuous—the last that had, as it were, a happy ending: the liberation of Europe.