This is a wonderful essay by King's biographer, Taylor Branch, on the 40th anniversary of King's assasination.

Quoted: Many of Dr. King’s closest comrades rejected his commitment to nonviolence. The civil rights movement created waves of history so long as it remained nonviolent, then stopped. Arguably, the most powerful tool for democratic reform was the first to become passé. It vanished among intellectuals, on campuses and in the streets. To this day, almost no one asks why.