[qam1]

The lessons of Rome are don't split the country into three parts

Not really, Considering after the split the Eastern Byzantine Empire lasted another 1100 years which is a pretty good run by any standards.

But I can see the USA breaking in 3.

The Left Coast
The "Red" States
Northeast

Of course The Left Coast will quickly go to the Mexicans the way SW France and Iberia went to the Visigoths after the split and the Northeast will fall apart like the Western empire with NYC becoming a decaying sewer hole just like the city of Rome at the end (though Bloomberg might turn it into that before our split)

The Red states should do fine.

[breakem]

The status of the eastern empire reinforces my point that developing population and cultural centers throughout the empire made it inevitable that Rome could not control the empire.

I'd like to split California into thirds, but I'd be in the wrong third.