Delta vs Piedmont
Without getting into a technical discussion of polyrhythmic syncopation and music theory, let's see if there is a simpler explanation of the differences between the two styles. Neither one is older than the other, as both developed around the turn of the century. Perhaps the biggest influence that created the two distinct styles is the population of the regions in which they developed.
The population of central Mississippi around 1910 was nearly all black farmers and sharecroppers. With very little social interaction with the sparse white population, the music that would become the Delta Blues was heavily based on the polyrhythmic syncopation (oops, said I wouldn't go there) of western Africa, field hollers, and early African-American gospel. The Delta style is derived almost entirley from African influences.
On the other hand, the population along the Piedmont was a mixture of races and backgrounds. In the cities along the Piedmont; Atlanta, Charlotte, Richmond, and Washington, D.C., blacks, whites, and recent immigrants lived and worked side by side. The interaction in the mills and factories, as well as the traveling medicine shows and Vaudeville troupes, exposed black musicians to the jigs and reels of Scottish and Irish descendants and the polka, schottische, and mazurka from east European descendants. As a result the Piedmont Blues took on a more melodic sound. Influences went both directions. If not for the African influence on string band and hillbilly music we'd have no bluegrass, country, or rock music today.
This blending of music from around the world to create the music North America is something I have written about in this space many times. Nowhere else on this little planet is made up of such a diverse group of people from all corners of the world. The United States and Canada truly are a melting pot of people, traditions and music. There literally is a whole world of music right here in our hemisphere, and the blending of those traditions and musics have given the whole world a host of wonderful music in return.
in the Delta style
in the Piedmont style