[jschveibinz]

No disrespect, but historical evidence does not support this argument. I've seen similar claims made in other threads.

Fertility rates have been decreasing (multiple factors) since 1850, even while general prosperity has been increasing. There is a connection between economic uncertainty and marriage/families over the short run. But the most likely causes of declining birth rates are cultural: modernization, freedom, female economic participation, contraception, later marriage or no marriage, etc.

The world has advanced, and the requirement to procreate has diminished. There is lower want/need from eligible individuals.

My parents had no money at all when they married and they were able to scrape together enough to raise three children.

[ilovecake1984]

You are missing a major driver of this. The main reason fertility rates have been decreasing is because of decreasing infant mortality. The number of children surviving to adulthood has been relatively stable until recently.

[jjk166]

And more specifically there is a delay between when technology lowers the infant mortality rate and it becomes culturally normal to have the smaller number of children leading to the same number of adult descendants, so you typically get 1-2 generations with way higher populations than preceding generations and then the rest after that is just this large initial population having a normal number of kids. This means you get massive populations and intense crowding decades after the fact.