Countries are just arbitrary here. What happens long term is there’s massive selective pressure because children of people that reproduce in wealthy economies are the only people to be around in 200+ years.

The USA as a whole has 1.7 births per woman which is really close to the ~2.1 needed. However that isn’t evenly distributed ethic Native Hawaiian and Pacific Islander’s living in the US actually sit just above replacement rate. Give it 200 years and that may very well increase.

Really 3 kids needs to be seen as normal long term because some people just aren’t going to have any.