If I recall correctly, Kevin Phillips attributed the American southern dialect to old East-Anglian dialect. At any rate most of the original white settlers in the south, Georgia especially, were subjects of "transportation" and subject to seven years of indentured servitude, or were Scotts-Irish recruited to be frontier settlers. Only a relative handful of ruling-class whites could afford nannies. And those families, the Washingtons and Lees for instance, were descended from landed aristocracy back in England who were on the losing side of the English Civil War. Take away the minority plantation owning families and the average white household at best could afford one, maybe two slaves as full-time field hands. Still, west African dialects probably did make their mark on southern dialects.
Actually, that makes a sort of sense. Those ruling-class whites who could afford nannies would be more exposed to non-rhotic speech -- therefore non-rhotic speech becomes associated with the prestige of their class.
