A rapper spits rhymes into a microphone. A DJ scratches a record back and forth against a turntable needle. Fans' feet stomp along to a stiff beat. These are the sounds of hip-hop. Hip-hop music busted out of New York City in the 1970s. Many young African Americans found their voices after stepping up to the mic. In the decades afterward, rappers and DJs took over the airwaves and transformed American music. In the twenty-first century, hip-hop is...