Population control is the rectification of overpopulation. Population control is the inevitable consequence of overpopulation, though population control can happen in various ways.
There are two general ways that population control can happen, which are artificial population control and natural population control.
Methods of artificial population control include enforced child number limits, sterilization, abortion, and killing. 'Voluntary population control' is an oxymoron, because most of the people that are breeding heavily are doing so intentionally. Natural population control is what happens when artificial population control is not applied to an overpopulated population. Though members of the inferior human species typically ideologically object to artificial population control, natural population control is much worse. Natural population control includes death by starvation, starvation-induced infertility, competitive killing, and competitive cannibalism.
Those aspects of natural population control, though horrific are, in fact, the more mild aspects of natural population control. The more serious aspect is that, when an overpopulated population exceeds the resource requirements that its environment can provide, it causes what may be called 'the locust effect', in which the enormous population strips bare numerous edible species of Earth, thus causing the extinction of the very food species that are needed for humans to survive. Such locust effects have, in fact, already killed off or endangered many wild animal species, many of them from the sea. Subsequent to the mass extinctions, the humans turn on each other and practice competitive cannibalism. It would be much better though if humans practiced cannibalism prior to wiping out other species, since that would allow the human species to survive the crisis, but humans will not do so because it is not in the nature of humans to be responsible.