Columbia Records started to produce and sell commercial discs in 1900, and within three years was claiming sales of two million per month. Not until August 10, 1920, however, when Okeh Records took Mamie Smith into a New York studio to cut Perry Bradford's "Crazy Blues", was the first black blues singer recorded.

Sex sells and it always has. In fact, from the vaude-ville of Sophie Tucker to the jazz-blues of Bessie Smith, there were probably more women singing sexually suggestive songs in the early decades of the last century than in our booty-shaking, permissive times.

en.wikipedia.org/wiki/Race_records

African roots, spirituals, work songs, field hollers, black folk ballads, instrumental gigs and the ministrel shows all played their part as building blocks of the blues. Yet before the blues came to prominence in the early years of the 20th century, another major development in African-American music took place. Known as rugtime, it was the forerunner of jazz.

en.wikipedia.org/wiki/Ragtime

en.wikipedia.org/wiki/W.C._Handy

By the end of the Civil War, African-American music had become a highly sophisticated synthesis of the traditions brought by slaves fron Africa and the european-derived styles and forms of the white settlers. After the end of forced mass immigration from Africa, when the slave ships had ceased their trade in human suffering, the old traditions were kept alive by oral transmission - just as they had been for generations via the griot tradition back in Africa.

en.wikipedia.org/wiki/Spiritual_(music)

www.negrospirituals.com/

Where did the blues begin? That debate has long exercised academies and ethnomusicologists and probably generated more heat than light. However, the truth is surely that the blues began several million times over. It was born again and again, every time another African gazed for the last time at the land of his or her birth as the slave ships hauled anchor and began their terrifying journey across the ocean into the unknown, leaving Mother Africa behind for ever. 

en.wikipedia.org/wiki/Slavery_in_the_United_States

www.blues.org/blues/background/index.php4

en.wikipedia.org/wiki/Willie_Dixon

www.rockhall.com/inductee/willie-dixon