How you control human population?

The main thing is to keep the Death Rate close to the birth rate.

In the past, you kill a lot of people with diseases and warfare. Those few who reproduce have 15 children, but most of the children die, are infertile or choose a life of celibacy.

In the present, you make people well educated, wealthy and secure and they decide for themselves to keep the number of children down to one or two. Both children grow up and do the same.