So.... has anything really changed? If the North represents what constitutes the big-government radical left now.... and the South represents small-government conservatives and anyone else that does not want government control of everything.... it seems to have not changed all that much. Especially considering how the Democrats are content to burn it all down in their fit of rage over having lost the 2016 election.
I have always had a maybe over-simplistic theory of why that is true, and some of it comes from my genealogical research.
In my research, I have found that in the minus some minority populations of Dutch, German, and a few other that
(1) Northern population was consisted of 90% English 10% Scottish and Irish. Realize that even though their immigration was to escape Britain, their inbred mindset was around support of a centralized monarchy
(2) The southern population was more aligned to a 50/50 split among England vs. Scotland and Ireland. These people are more independent minded in the spirit of William Wallace. They much more preferred minimal government, and as people strongly hated people meddling in their affairs.