Alright. Basically modern day American evangelicalism is NOT the churches of the South from the Civil War to segregation exported to the rest of the country. In fact most Southernors in the 19th century were mainline Protestants, mostly Methodist, Presbyterian, Episcopalian or traditional Baptist (which was more associated with mainline back then.) Pentecostals and most fundamentalist denominations today didn't even exist at time.
Even during the Jim Crow heyday, this was mostly true. The KKK membership was largely Methodist (somewhat ironic since the United Methodist Church today has a pretty large number of black membership, especially in the South, but at the time it didn't exist and was a bunch of smaller factions), and the Southern Baptists were almost mainline and no more conservative than most modern day mainline denominations. Even during the Civil Rights era this was true. The SBC liberalized at the same rate as other mainline denominations until the 80s when this started being reversed with a conservative takeover and shedding of the more liberal churches to more liberal Baptist associations. In 1976 Jimmy Carter wasn't too odd in the SBC (he later joined the American Baptists, a more liberal denomination.) In fact during the Civil Rights Movement most of the evangelicals were on the pro-civil rights side, which makes sense as they were basically the only ones with integrated churches back then. Furthermore most evangelical denominations that ordain women, even conservative ones, did so far before most mainline denominations today did.
Most modern day evangelicals and fundamentalists come from the Great Awakenings, which was hardly something that existed only in the South (the
burned over district is obviously not in the South.) Sure the South was affected like everywhere else by it, perhaps even disproportionately, but it wasn't something exclusive to the South that gradually trickled to the rest of the country.