First there was the 50th anniversary of the Civil Rights Act last July, one of the central achievements of Martin Luther King Jr.’s crusade. Then, last August, there was what has come to be known simply as “Ferguson,” the bitterness over a killing that reminded us that issues of race, violence and nonviolence are still simmering, still ready to explode at any time. And now in January, a major film called Selma will be released nationwide that dramatizes a key moment in the evolution of King’s struggle.

Selma was a turning point in King’s life as well, according to Taylor Branch, whose three-volume, 2,500-page chronicle, America in the King Years, is one of the landmark biographies in American history.

March, 1965. King and his demonstrators had been beaten by the police, driven back from the Edmund Pettus Bridge, back out of Selma on a day called “Bloody Sunday.” But suddenly there was a chance to cross that bridge again. As Branch describes it, “King stood stunned at the divide, with but an instant to decide whether this was a trap or a miraculous parting of the Red Sea. If he stepped ahead, the thrill of heroic redemption for Bloody Sunday could give way to any number of reversals....If he stepped back, he could lose or divide the movement under a cloud of timidity.” King stepped forward and nothing was ever the same.

Not just in the civil rights movement, but as Branch told me when I spent the afternoon talking to him recently, nothing was the same for King either.

“I think what changed is how much he was willing to risk for the belief that he had formulated,” Branch says. “After Selma, I don’t think he expected to live a long time.” ...