What is most likely to control overpopulation of the earth?

A viral epidemic for which there is no vaccine.

Donald Trump.

War, famine and disease - the usual things.

A flu mutation.

Two national leader, each competing against each other for a position of influence and totalyl devoid of any common sense. contemplating a button which would settle the argument once and for all.
Eventually one of them reaches forward and presses the button.

An asteroid

Vaccines

Poverty, disease, and war

Advances in food production.

Nuclear war.

Ageing population

Ha.... Discover the future is now, and realize the tech we're sitting on presently 2018.. spread TF out once said tech creates true autonomy and freedom... Yadayada... Give me water, or give me death. Oh hey! https://m.youtube.com/watch?feature=youtu.be&v=TnrWqp0f6IE