During the 1990s massive changes took place in hip-hop culture. Hip-hop started out in the South Bronx as a street-born cultural movement grounded by what have become known as the four pillars of hip-hop: DJ-ing, MC-ing (later known as rapping), breakdancing, and graffiti art. By the 1990s many of the original elements of hip-hop music had been stripped away, and rap music had emerged. Rap was a force in the 1980s, with Run-DMC and LL Cool J spreading the Bronx-born sound from Brooklyn to Beverly Hills, but few would have expected performers such as MC Hammer and Vanilla Ice to make rap music a central force in pop radio. By the 1990s the authentic voice of ghetto youth had become mindless jingles with polished beats that suburban teenagers nationwide could dance to at school dances. Rap made its way into movies and television...