Selective memory, it seems, is a global phenomenon. Think of Turkey and its blank spot where the Armenian genocide should be. Or Japan with its squeamishness about its aggression and mass murder in China. It starts as a basic human impulse to take the sting out of defeat or to avoid admitting some atrocity. But it’s also a way to help cope with a difficult present. And like a growth on a tree ring, it can keep the past off-kilter until some future generation is brave enough to right it.

“In most countries you are more likely to get evasion and nationalistic versions of history than tough grappling with the darker parts of your past, and the U.S. is no exception,” said Gary Bass, a professor of politics and international affairs at Princeton.

In the United States, the Civil War remains “the most divisive and unresolved experience Americans have ever had,” according to David Blight, a historian at Yale. “The Civil War is like a sleeping dragon. If you poke it hard enough, it will raise its head and breathe fire.”

That is, in part, because the loser was allowed its own interpretation. The South, facing catastrophic loss of life and mass destruction on a European scale, wrote its own history of the war. It cast itself as an underdog overwhelmed by the North’s superior numbers, but whose cause — a noble fight for states’ rights — was just. The North looked the other way. Northern elites were more interested in re-establishing economic ties than in keeping their commitments to blacks’ constitutional rights. The political will to complete Reconstruction died.