How did the 12 bar blues start?
It started when the Africans were sold as slaves to America. The Africans brought their syncopated rhythm from Africa and combined this syncopation with words to produce work songs. As the slaves worked, they sung these songs. In these work songs, the Africans used a concept called call and repeat, the foundation of the twelve bar blues. Eventually, the work songs evolved into what we call the twelve bar blues.
