[pjc50]

The usual one is "availability of contraception and related education for women". I don't think even the fundamentalist states have chosen to and managed to reverse that. Least feminist most collapsed country Afghanistan is still falling: https://www.macrotrends.net/global-metrics/countries/AFG/afg...

We still don't know what a "modern depopulated country" might look like, that is a whole country where the population is more than 10% below its peak level by natural decline. It's visible in some areas and cities, but not the whole country level.

[AnimalMuppet]

Plausible. But what about sub-Saharan Africa? Do they not have access to birth control? (Or are they falling too, just started later?)

[pjc50]

Much less so, it's extremely poor and more likely to be starvation or war limited. But even there it's going down.