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.
Qin or Qing? Because those two dynasties are separated by about 2000 years. For reference, this is the guy depicted and he was a legalist of the state of Qin. He’s a pretty interesting dude, with the foundational work for Chinese legalism being attributed (at least in part) to him.
Also he was executed by being torn into pieces, which is pretty metal.