Actually, the predominat pre-19th century immigration population in the southern U.S. states was Scots/Irish. The southern drawl is different from state to state, but is noticeably similar to Scot and Irish inflections in many locations. This special, archaic variety of English is known as Appalachian English. It preserves many archaic features that date back to earlier stages in the development of English in Britain. Additionally, th influence of the black, mainly slave population of southern dialects is significant. Black English developed in the Southern states when speakers of dozens of West African languages were abruptly forced to abandon their native tongues and learn English. Slaves from different tribes couldn't communicate with one another--in fact, masters deliberately tried to separate slaves who could speak the same language. Since the Africans had to communicate with one another, as well as with the whites, a kind of compromise language evolved on the basis of English and a mixture of the original West African languages. Such a makeshift, compromize language, used as a second language by adults, is known as a pidgin. When a pidgin becomes the native language of the next generation, it becomes a creole--a full-fledged language. The African-English creole in the American colonies evolved into today's Black English and had a heavy influence, paradoxically, on today's southern inflections... (Thanks to Linguistics 201, The Dialects of American English)