A situation where the population of an area returns to subsistence living after experiencing a sharp population growth. This is because food reserves and agriculture become unable to support the huge population, causing hunger and poverty that leads to a downward spiral. It was first identified by the Reverend Thomas Malthus after he noticed that population growth is exponential but the growth of food supplies was arithmetical.

The work of Malthus is frequently used today in arguments that support birth control and population control.