Complex sentence: Prince's rephotographs led to his series known as the Gangs, which followed the same technique of appropriating images from magazines as the Cowboys did, but now the subjects moved from advertisements and mass media toward niches in American society.
Split into simpler sentences: Prince's rephotographs led to his series known as the Gangs. The Gangs followed the same technique of appropriating images from magazines much as the Cowboys did, but now the subjects turned away from advertisements and mass media and looked towards the niches within American society.