1920s: Through live performances and recordings, Ma Rainey, Bessie Smith, and Louis Armstrong help to popularize blues and jazz as distinctive forms of black music.

1980s: The black group Sugarhill Gang inaugurates the history of hip-hop with their single "Rapper's Delight," a multi-platinum seller and radio hit. From the Sugarhill Gang come the works of Grandmaster Flash and the Furious Five. In the early 1980s, this group take the lead from the Gang and developed rap, integrating the sounds of a live disc jockey scratching on wax on their albums.

Today: Hip-hop and rap music, though originating from black performers, are widely embraced by white audiences and practiced by white performers such as Eminem.

1920s: The Ford Motor Company introduces the Model T and produces their 15 millionth Model A.

1980s: Worldwide earnings at Ford reach an all-time high of $5.3 billion in 1988, the highest to-date...