Neat - For neat stuff you found

Good article, but no mention of Fallout even once?

Historically, states have mapped pretty well to watersheds with navigable rivers, since that was an important form of transport. Basically, the ocean and its coasts were how one did transport, and rivers were how you connected to that inland.

If someone controlled your downstream access to the ocean, they had a stranglehold on you, and so either you or them would fight over it and come out on top for control of it.

Prisoners of Geography makes an argument that all state geography, even today and in the future, is determined along these lines. I think that that's not actually a reasonable take, is too geographically-determinist

motorized road and rail have made overland transport a lot more practical in recent years

but I do think that it's still something of a factor and that it's interesting in looking at why today's state boundaries existed as determined in the past.

According to it, that's why China has historically cohered along one giant state

it has a huge watershed along the Yangtze River, and you can expect one state to sooner-or-later wind up in control of it.

Same thing with the Mississippi River watershed in the US.

Europe's geography, on the other hand, has many small watersheds, which historically led it to have many small kingdoms.

While I'm not sure that I buy into navigable rivers being as important in modern times as they were historically, I would point out that in a post-apocalyptic scenario in which you had civilizational collapse, if transport systems broke down

how well would the global crude oil extraction and gasoline refining and distribution system work? Or widespread electricity generation and distribution?

I could very readily imagine river transport being more relatively-important than it is today. That map doesn't really reflect US watersheds.