In the long run, a worldwide population crash is rather likely. This is a thought experiment on the second, third and more order of effects of what will transpire as a result.

First, market sizes will shrink across the board.

There will be more money for everyone but they are worth less.

More people per capita will be end up working in health care, begrudgingly so, simply because it pays well.

Competition will be less fierce because there are lesser people to compete with. With that cost of new life adjust down a bit, people start to give birth again.

Population will be sustained by uncompetitive people, given birth by uncompetitive parents who are willing to let nature runs its course.

In attempt of trying to boost population, socialism (maybe even communism) will have its days again. This in turn drive overall wealth smaller through inferior resource allocation. Places that do will succeed in breeding but suffer in wealth per capita.

Ideologies will emerge to prioritize breeding over economic wealth. The songs of sacrifice will be sung, not only by children but by peers.

Some of these ideologies will also realize that education for all its virtues is counter effective against the agenda of breeding, but reluctant to admit it openly. They adopt implicit policies that deprioritize formal education, opting for "nature's ways" approaches when it comes to population indoctrination.

Corners of the world that maintain capitalistic policies remain competitive but continue to cope with dwindling population. Parts of the world that are breeding become their commercial targets. They continue to reap most of the wealth and sit on top of the social pyramid.

Wealth gap grows to a boiling point, another class-war erupts with devastating consequences.

Leaders from all camps come to the conclusion that all classes need each other. The rich need markets to serve; the poor needs people smarter than them (but won't admit it).

"Living together" is too hazardous when information flows freely. They decide that it's better to divide people neatly by classes via social engineering in order to avoid inter-classes interactions. Censorship becomes active throughout. It's agreed that this is practiced only until "the population has recovered", of which the precision is not defined.

Nothing is more permanent than temporary policies. New age of caste systems emerge.

Over time, population recovers. The reasons hierarchies are forgotten, demands for equality get violent. The cycle repeats.