[xyzzyz]

> This dynamic works because unlike pre industrial malthusian times, cities do not rely on birthrates for population growth.

The same was true in pre-industrial times too. The cities have always been population sinks, and failed to reproduce naturally. They have always been supplied by the constant stream of people from countryside.

[ummwhat]

I forget exactly when this happened or which data set it's in, but at some point sanitation and medicine got good enough that cities aren't a population sink per se. They can have around equilibrium birth rates.