the us has an advantage of having lots of good dirt. the south is fertile, the midwest is fertile, the far west is fertile ... we are talking tons and tons of really good dirt. while much is made of inginuity or exceptionalism or whatever, nothing beats have oodles and oodles or really good real estate.
ive walked around a fair bit in scotland, and the world is a different place, but chopping up the island seems like a head scratcher to me. its got its two great cities, a wonderful but often harsh countryside, it just seems that anglia makes them more whole.
when I think of nation I think of things from the bottom up:
1. water
2. good dirt
3. transportation, things like ports and rivers.
or at least land amenable to things like road and rail
the US pretty much has the best real estate on the planet, and could well afford subdivision. obviously it would involve backing down from the mega-superpower thingy and ceding is international military presence to a confederation of sorts, a tough pill for such a highly militaristic society.
It is something I used to think of much, and even at state levels (NoCal vs SoCal), states straddling mountains so different on opposite sides (WA, CA, OR)
I dont have a feel for the south, but it does seem there is an area of cohesion. There are less related but highly dependent areas, mineral areas so to speak, WY ... what do you do with WY?