Hi, and thanks for giving me the opportunity to answer your question.
The accents heard in our southern states come from two separate origins. The 'drawl' that is common among Caucasian southerners originates from England. Between 1642 and 1675 the Royalists, or Cavaliers migrated to the southern coastal states, bringing with them their servants, and their south England drawl, or a drawing out of the vowels. They also brought such word aberations, such as 'aksed' instead of 'asked', and the word 'ain't' instead of 'isn't'.
The other influence in the southern states is the so-called 'Black English'. This developed as a result of so many African-American immigrants, slaves, being required to attempt to communicate with their masters, and with each other...none of whom spoke their native language or dialect. This resulted in the the loss oif final consonants, among other things. ie 'po' instead of 'poor', and 'nothin' instead of 'nothing'.
Depending upon the upbringing, social and economic status, and region of the South, you can hear both influences quite clearly!
Finally, I'm going to refer you to a great online article that goes into both accents in more depth:
I hope that this has answered your question. Please let me know if there is anything else that I can do to help.
Good luck, and best regards,
(I would very much appreciate your clicking on the green 'Accept' button, as it is the ONLY way that I get compensated for my time. Thanks VERY much!)