A useful source on this issue is Peter van der Merwe, Origins of the Popular Style: The Antecedents of Twentieth Century Popular Music. It is a well thought-out argument which proceeds from musicological rather than sociological grounds, and makes important suggestions about the route by which European and specifically Scots/Irish folk music (in turn influenced by Arab music) had a formative influence on the Blues. I can't summarize the argument from memory but anyone with a scholarly interest is recommended to pursue it. (I reviewed it in the Journal of American Studies, some years back, if you have access to that journal).