> If we swapped eastern Canada and western Mexico into the United States, it would be difficult to build the sort of common empathy and identity that countries require to persist.

How would that be harder than it is with the parts of Eastern Canada and quite giant portion of Northern and Northwestern Mexico, including over a quarter of its west coast, that actually were “swapped into” the United States?

> how would that be harder than it is with the parts of Eastern Canada and quite giant portion of Northern and Northwestern Mexico, including over a quarter of its west coast, that actually was “swapped into” the United States?

Territories. Not substantial foreign populations. Hence the parentheticals.

Mostly those borders were always going to be nonsense no matter who came up with them. One village is this group, another village is that group then the next is also to the first group. It's like that in almost every country. Obviously the British and French really screwed up a lot of stuff but there's a reason people who criticize the borders never offer any suggestions of where they actually should have been.