For the past 40 years, South Central L.A. has been the nexus of a bloody feud between street gangs the Crips and the Bloods. The conflict’s roots are in the 1950s, when young African-American men, excluded from such organizations as the Boy Scouts, formed their own clubs. But societal and economic factors fostered the escalation of a civil war that has taken 15,000 lives in the past 20 years. Director Stacy Peralta brings the same dynamic style that he forged in his skateboarding documentary Dogtown and Z-Boys to the subject, blending often shocking archival footage with interviews to etch a graphic portrait of tragic, self-perpetuating violence. Tuesday, May 12, at 10 p.m., PBS; check local listings