According to PBS.org, the blues has its roots in field hollers and spiritual chants sung by African-Americans predating the Civil War. A combination of European structure and African call-and-response, the blues reflected hardships felt by people coping with a rough reality. Bukka White and Robert Johnson were early blues artists.
Blues form has made its way into various other genres of music--such as rock, gospel, country and jazz--most notably its 12-bar structure and harmonic chord progressions.
Rock and roll is a direct offshoot of the blues. Artists such as Chuck Berry, Little Richard, Led Zeppelin and the Rolling Stones incorporated the instrumentation, vocal styling, form and raunchy lyrics of blues into something new.
The migration of African-Americans to northern cities after emancipation led to diverse blues styles developing in different cities, most notably Chicago, Detroit and St. Louis.
The blues paralleled black and white integration in America, according to Stax Records songwriter Al Bell. White audiences embraced black music and it became popular on the charts.