One of the greatest of American stories has found its great chronicler in Taylor Branch. Beginning with Parting the Waters in 1988, followed 10 years later by Pillar of Fire, and closing now with At Canaan's Edge, Branch has given the short life of Martin Luther King Jr. and the nonviolent revolution he led the epic treatment they deserve. The three books of Branch's America in the King Years trilogy are lyrical and dramatic, social history as much as biography, woven from the ever more complex strands of King's movement, with portraits of figures like Lyndon Johnson, Bob Moses, J. Edgar Hoover, and Diane Nash as compelling as that of his central character. King's movement may have been nonviolent, but his times were not, and each of Branch's volumes ends with an assassination: JFK, then Malcolm X, and finally King's murder in Memphis. We know that's where At Canaan's Edge is headed, but it starts with King's last great national success, the marches for voting rights in Selma, Alabama, in 1965. Once again, the violent response to nonviolent protest brought national attention and support to King's cause, and within months his sometime ally Lyndon Johnson was able to push through the Voting Rights Act. But alongside those events, forces were gathering that would pull King's movement apart and threaten his national leadership. The day after Selma's "Bloody Sunday," the first U.S. combat troops arrived in South Vietnam, while five days after the si