And before you say: oh, they're different from us, remember that Sarajevo was a modern city that hosted the winter Olympics 8 years before brutal war broke out. Most of its citizens thought the idea of war happening was absolutely preposterous, until it wasn't.
Are you still so sure about the idea of internal civil strife being "unsubstantiated fear mongering"?
And by the way, race-based civil conflict is only a small part of the structural problems I'm worried about. There are multiple deeper, more dangerous threats on the horizon.
For example, are you sure that Trump will peacefully vacate the office if he loses the election? If not, what exactly do you think will happen then?
Finally, not that this matters a whole lot to me, but to provide you with "substantiation" that you may accept, many mainstream media outlets have covered this in detail in the past year or two. Here are just a couple, Google keywords such as "US civil war 2" (just "civil war" turns up Avengers stuff) and "boogaloo" for more mainstream media coverage:
https://www.washingtonpost.com/politics/in-america-talk-turn...
https://www.macleans.ca/society/america-is-deeply-divided-an...