When did Southern American English really begin

This paper uses the Corpus of American Civil War Letters, comprising several thousand documents written by minimally literate privates in the conflict, to analyze grammatical features such as you-all and fixing to. The authors respond to the proposal of Bailey (1997) that white Southern American English shifted rapidly and radically in waning decades of the 19th century, and show that the shift was not as rapid, but may have been quite as radical, as Bailey argues. That is, the grammar of white SAE had more continuity between the antebellum and post-bellum periods than Bailey posits, but began becoming distinct from the English of the northern U.S. earlier. The paper concludes that white SAE “began” prior to 1850.