(ASB in bold)
Jim Crow never ends, thus leading African Americans to be increasingly militant, and carving out an unofficial
Black Belt nation, which takes advantage of the Second Amendment to stockplie weaponry, which in turn inspires "white nationalists" to be even more violent than IOTL, and to boot you've got black militants in northern cities commiting actions on behalf of their southern brothers, and all the bad publicity leads to a Boycott USA campaign in other wealthy countries, thus crippling the economy, and things just kind of go downhill from there.