Ok, let us look at 8 years ago. Igor "Strelkov" Girkin with 51 soldiers started from Crimea and went to Sloviansk (Slavyansk) and captured the city with 140 000 citizen. That action started the Donbas war. OK, there was kind of anarchy because there was no President (Yanukovich has escaped to Russia before the war and it was before acting president Turchinov). But anyway what will happen with 52 armed men if they enter into any 100k+ USA city for the sake of separatism? I bet they will be killed in first hour before even entering the city and all separatism sympathisers will be punished as well.
If the US was to go through a period similar to the post-Soviet breakup, I would be very pessimistic on how violent it would be, owing to the numbers of weapons present in the country.
I really think Donbas would have been more peaceful and less separatist if there had been more weapons before Strelkov's campaign of 2014. I can tell even more - there would be no Bucha massacre if any household of Bucha had something more powerful than a shotgun (50m effective range). And by the way, getting allowed for using even a hunting weapon in Ukraine requires passing through tremendous bureucracy.
For example, if I want a shotgun to practice shooting at plates and bottles, I need to declare my goal as becoming a hunter. Becoming a hunter requires passing an exam on fauna species (for not shootng a Red Book species, obviously). But I don't want to be a hunter because Ukraine is not a USA and seing wild animals in forest is a rare event (believe me, I am living less than 1 km to a nearest forest and it is a tough natural forest, not a park with sparce trees). And going through hunterness is not the only bureaucracy obstacle to becoming an owner of firearms.
Imagine seeing a military colon going to capital of your country at the assault rifle range and having no ability to do anything except of wishing good luck to the capital, because of the decisions accepted in the capital.
They would have guns too, mr. Putin gave them much heavier weapons anyway.
I would see a pro-Russian citizen of Ukraine with an ability to have a gun here but with no ability to have guns in the country they prefer - Russia.