I mean, there’s an infrastructure problem that’s worth considering. With low enough population density, it could become no longer feasible or worth it to maintain large-scale, country/globe spanning infrastructure projects such as power grids or undersea fiber optic networks. This infrastructure didn’t matter much a few thousand years ago, but it’s pretty critical now, so the same rules don’t necessarily apply.
I don’t know how likely I consider this outcome to actually be, as you’d need a very steep decline, but it’s at least worth keeping in mind.
NA Racists getting angry about pros from other regions ruining the local scene