In the real world, secessionism appears to be on the rise, with Brexit and the ongoing Spanish situation. Let us hope that Scotland is next, and we have an increasing number of templates for peaceful devolution of sovereignty.
Edward Longshanks took (rather forceful) exception to Scots secession. Abraham Lincoln took (even more forceful - why was the Anaconda Plan abandoned, anyway?) exception to Southern secession. I know Texas secessionists ( glancingly, not well ) and I tend to quote Sam Houston to them. They're not to be taken seriously. Yet.
I see no reason to think the pattern would abate. Brexit isn't in that set because the Eurozone is barely even a convenient fiction. It's a con job, the sort it would take an H.L. Mencken to characterize properly.
I can't even choose a pet narrative of how it is we should be organized in that way. I just know how it is - we're in really big chunks. I credit the sort of peace we now enjoy somewhat to the size of those chunks.