The religious nutters who ended up in new england because they got squeezed out of Europe... kept getting squeezed west (the bible belt was west when they started the squeezing), like later on how the proto-mormons split into a relatively laid-back community in idaho (if I recall correctly) and the real nutters in utah.
The bible belt is the super fertile land along the ancient seashore that ended up growing slave-owning religious nutters.
Sorry to nitpick. The laid-back people are in the Midwest. Idaho is about like Utah. The Mormons in the Far West both had the authoritarian Young followers and an infusion of Southerners who were conservative as leaders.
I’m convinced the real dividing line in American religion is slavery. The evangelical and Baptist denominations currently forming the Republican base are part of a cultural constellation that is centered in the South. Churches in the South changed their teachings to accommodate slavery and authoritarianism, and to demonize outsiders such as Catholics and Mormons. This creates a deep difference between the fundagelicals and mainline or liberal Protestants.
The mainline churches are losing members, and the fundies are gaining some by presenting a pop religion with little theological consistency. Fundagelical religion can be very superficial.
There are exceptions to this rule, like socially liberal Mormons in Salt Lake City and social conservatives in the Black churches, but overall the pattern is for a fundagelical culture that’s pretty much the descendant of the Confederacy, even though migration has carried it to other places over time.
It’s hard to describe it until you see it - if I had to predict a common denominator that predicts who will stick to a fundagelical church, I’d look for an acceptance of cruelty in child rearing and from authority figures. This tracks with the hierarchy of human value that the slave owning religions endorsed, while the abolitionist religions became today’s social liberals.
I’m painting with a broad brush here, but this matches what I’ve seen on the ground as I moved around the country.
Chrissy Stroop on Twitter started the #Exvangelical tag and they go into a lot of detail on how the hardcore part of this culture works.