It won't surprise me if
the continental 48 states of the USA
go through a permanent division at some point.
Population growth has much to do with it.
There are just too many people,
too many centers of industry,
too much darned traffic ...

Our part of North America has always had polar opposites and conflict,
there is nothing remotely new in that.
What is more to the point is the sad opinion
of Yeats about his Ireland:

"Great hatred, little room,
Maimed us from the start.
I carry from my mother's womb
A fanatic heart."

A single centralized power/government can do so much,
and no more, while the population grows and grows.
I don't know if I'll be here to see it,
but at some point,
the continental 48 will have more than one government,
and the border will be,
not only at Mexico,
but within the 48 somewhere.