Well, I grew up in the 50’s and there were 4 kids in our family. Most of my friends were in families that had at least 4 kids. One of my friends was one of twelve kids. I think the Sexual Revolution and the rise of Feminism are the main factors in the decline in our population. And don’t forget that Third Ril of Liberalism in the 60’s, ZPG. Zero Population Growth. Most families thee days are just relaxing the Mother and Father with only having two kids. Some of us were only able to have one child. I hope future generations will see the benefit of kids.......my generation was made to feel guilty for wanting kids at all.
I would argue this is what is really behind Japan's stagnant economic growth in recent years. Russia is now in serious trouble as alcoholism and other health issues compound the birth rate problem.
China really shot itself in the foot with its one child policy. China forcibly joined the declining birth rate trend of the West before it fully developed, which is leaving it with the worst of both worlds.
Feminism, contraception and abortion have contributed, but are not the root cause of the trend. The good news is rates are declining worldwide and the planet will probably reach equilibrium around 2050. Without the "population bomb" what will the doomsayers have to complain about? Oh, yeah, globull warming.