What's happening in China is slightly different. For the non-excluded population, there's generations now who do not have brothers, sisters, cousins, aunts or uncles. Add on top of that selective abortion for the male preference, and no social safety net, and you've got the most interesting sociology experiment in history.
Japan, Russia and Italy aren't being forced through it by an authoritarian government, but are rather experiencing ennui at a social level.
America is the same, though immigration helps hide the problem. I have one sibling. My parents had six each. Their parents had between 6 and 12.
The rapid expansion of the last two-four hundred years is definitely slowing down throughout most of the world.
It's less about population size, and more about ecological footprint of the population. Per capita, rich nations and rich populations within developing nations are the ones having the biggest ecological impact: https://overshoot.footprintnetwork.org/newsroom/country-over....
