Zaire ’74—a three-day music festival for which dozens of top-flight performers, some African, others American, convened in Kinshasa a month before Muhammad Ali and George Foreman’s “Rumble in the Jungle”—took place during a period of intense political and artistic ferment in American music. Jeffrey Levy-Hinte’s document of the festival, assembled more than 30 years after the fact (from footage shot by, among others, Albert Maysles and Roderick Young) and bookended by a pair of searing performances by Brown, captures the event in all its tension, ecstasy, sweat, and uncertainty: Ali trades mock-punches with the lead singer of The Spinners, Bill Withers brings down the roof with a devastating rendition of “Hope She’ll Be Happier,” and revolution is in the air throughout. Soul Power is a revealing portrait of an era as manifested by some of its most dynamic and politically engaged performers.