I doubt that the "collapse" will involve competing armies staging themselves for battle. Rather it will be various left- and right-wing militas in urban street brawls. Think of Northern Ireland--but in many more locations.

It will be harder to run a modern economy in this environment. Most citizens will learn how to keep their heads low. There will be official and unofficial governments.

But democracy is not forever. It can evolve into an oligarchies. And not all oligarches are bad for their citizens. Fewer rights, but a certain degree of peace and prosperity. Isaac Asimov prophecized that democracy has shelf life of 2 or 3 centuries:

https://medium.com/tiered-democratic-governance/asimov-foundation-democracy-26ea4578e49d

To me, the sign is that Mr. Trump would not have been elected to anything 15 years ago. Things have changed in the USA. The November 2021 gubornatorial election in Virginia is a sign that American democracy doesn't have much "self-correction" left.

Think Northern Ireland.