"250 years is not a particularly impressive amount of time for a country to not fall apart." ?

Sure it is, it's very impressive.

What other nations have lasted that long?

Chinese Dynasties usually collapse within that range.

Aside from the UK, maybe Sweden (?) which have been fairly contiguous, most nations are more short-lived. France is on it's 5th Republic in the same time-frame.

America is way more than the gong show in charge right now.

Most of the 'tests' of it's integrity are due to really just that one guy.

But you're right to point out inherent problems with the Union.

Because EU is not a 'right wing flag waving' entity, we don't really think about it in terms of 'nationalism', but the EU has among the loudest, most clearly visceral and virulent nationalist supporters.

You can say anything you want about national governments but critique of the EU is met with a lot of rancour.

I've worked for EU bodies, it's full of well meaning people and it has tremendous value as an economic unions, but as a political entity it has existential flaws, too many to name, and it is absolutely an elitist project and it absolutely has a 'regulate first' attitude, which is quite upside down.

'Doing The Stuff' matters 10x more than 'Talking About The Stuff'.