There was little violence after the acquittal of Trayvon Martin's killer. Peace prevailed when four other unarmed black males were killed by police in recent months, from New York to Los Angeles.
Then Michael Brown was gunned down in Ferguson, Missouri. And waves of riots have convulsed the city.
Why Ferguson? Observers cite a convergence of factors.
Brown's killing happened in broad daylight, and the body lay in the street for hours. Police responded aggressively to protests. And some say people were simply fed up with the toll of killing after killing of unarmed black males.
Kevin Powell, president of an advocacy group, is heading to Ferguson as a peace activist. He says one reason for the riots is that it appeared that local authorities didn't care about the community.