It is a conundrum. What makes a country, it's parts, but it's parts all the way down to the individual. At what point does it 'break apart'. Or re-form.
Didn't Monico try to secede from France?
Wasn't there a couple provinces in Spain that were trying to leave.
And Ontario has had some movement to leave Canada for awhile.
It seems like every group, no matter the size, will eventually have some sub group that wants to leave. It almost seems like human nature, as soon as you feel like the 'group' is infringing on you as 'individual' and enough people that feel that same way will 're-group' and form a new entity.
The US holds itself on a pedestal. But I really think it is more geography that lead to the little cohesiveness it has. Lots of ocean boarders, weak countries on the others.
Throw the US into the middle of Europe, with same pressures from all around, and internal conflict, and then does it become the Austria-Hungary Empire? What about the US is making it special, except luck.
I don't have any answer.
But I do think that the US is 'stronger together' no matter what the internal disagreements. Just as a Nation, with the need to organize, defend. Given the geography, The US States are stronger together. Any break apart would reduce the remaining factions to less than they are now.