Rapidly expanding population of any species to the point of overpopulation leads to a population collapse. This seems to be a rule of nature. The extreme recent example is the passenger pigeon which became extinct. In humans it is caused b prosperity becoming general, especially with the minimization of disease that modernity has provided. In the richest countries, having children has become a net expense and a stumbling block to more prosperity for individuals thus fewer are born and the rich countries are overrun by the third world which is still having huge numbers of children and for which more children are still on net a financial benefit. As those populations begin to partake of the prosperity of the advanced countries, childbirth decreases among them, too. Overpopulation is self-correcting. Bill Gates doesn’t have to kill off 6 billion people to solve the “problem.”
The shortcut for the underdeveloped country populations is mass migration to the richest countries. Since 1990 over 40 million LEGAL permanent immigrants have entered the US. Millions more enter illegally.
What we are seeing now here and in Europe is a harbinger of much greater flows in the future. It is Camp of the Saints.