Pioneering skateboarder Stacy Peralta has become an impressive filmmaker over the past few years, directing two great sports documentaries—Dogtown and Z-Boys and Riding Giants—and writing the script for the fictionalized retelling of the Z-Boys' story, Lords of Dogtown. With his latest doc, Crips and Bloods: Made in America, Peralta turns his lens on the gangs of Los Angeles and their conflicts. It's a story of "five generations of urban soldiers," narrator Forest Whitaker grimly notes at the outset, and of a "bloody, 40-year feud [that] has taken five times as many lives as the long-running sectarian conflict in Northern Ireland."

The best parts of Crips and Bloods: Made in America examine how institutionalized racism encouraged Los Angeles' gangs to develop ("Part of the mechanics of oppressing people is to pervert them to the extent that they become the instruments of their own oppression," says one former gang member), how those gangs evolved from clubs of neighborhood boys into veritable armies, and how events like the Watts and Rodney King riots crystallized the city's state of urban warfare. The subject matter here is moving and damning, and many of the interviews with current and former gangbangers are riveting. Unfortunately, the film takes a dive for its final third, getting all sorts of preachy and manipulative—Peralta proves far better at chronicling events than trying to shape them.