From wiki:
Southern dialects originated in large part from immigrants from the British Isles who moved to the South in the 17th and 18th centuries.
African American Vernacular English
This type of Southern American English originated in the Southern States where Africans were at that time held as slaves. These slaves originally spoke indigenous African languages but eventually picked up English to communicate with their masters and one another. Since the slave masters spoke Southern American English, that is the dialect of English the slaves learned.
