Assuming you mean the United States "Southern accent":

More can be written on this, but you might like to start with some existing discussions.

The FAQ has a section on English accents and dialects at "Accents and dialects" . There are many about American accents, but there's this about the South both pre-Civil War and post-: "How has the American Southern accent changed since the Civil War? Before the war, was it perceived as prestigious in the North and elsewhere?" by /u/tropical_chancer .

Outside the FAQ: 'How did the "Southern" accent develop on the U.S and what accounts for its variation across the region?' by /u/zabulistan (though it's a bit loosey-goosey and depends on links).

/r/linguistics appears to be an approved subreddit to point to per this, so "How did the "Southern" accent develop on the U.S and what accounts for its variation across the region?" , specifically the answer by zabulistan (there's a lot of dross in this discussion).

This is not to discourage discussion. Further questions, data, and debate are welcome.