From what I understand, the rural south has been pretty homogeneously Baptist since the 19th century, prior to the rise of Pentecostals and the Evangelical movement. Other Protestant denominations, like Episcopalians and Methodists and Lutherans, seem much more widespread in northern and midwestern states than in the South.
How did a movement that first landed in New England take over the South?
The two sources I have looked at that trace the development of religion in the colonies somewhat address your question. Beginning with the First Great Awakening, the southern colonies were influenced both by European Protestantism and their understanding of their new lives in North America. The Baptist sect of Protestantism allowed southerners to adopt Christianity to fit their understanding of the world, most specifically with slavery. The First and Second Great Awakenings saw a huge jump in Black participation in Protestantism. Baptists in the southern colonies, and later states, adopted Baptist lessons to suppress Black religious freedoms and reinforced the social status quo.
The Rebellion of Nat Turner solidified the importance of continuing the religious and social suppression of Black enslaved persons.
I'm sure others can provide a more in-depth answer, but I hope this gives you a starting point.
William Warren Sweet, The Story of Religion in America
Thomas Little, The Origins of Southern Evangelicalism: Religious Revivalism in the South Carolina Lowcountry, 1670-1760