I believe there are many 'southern' accents. Furthermore, I believe they are descended from the various people of different ethnicity that originally settled the various regions. Probably the most manufactured American accent is the standard TV news accent. My ears began to open when a Carolinian gal complained how I spoke in diphthongs all the time as do all Yankees. It seems Yankees can't make a simple vowel sound, they always make it like two vowels together. All the time I thought she had a drawl when it is the other way around.
One of the greatest complicators of vowels was Katherine Hepburn.