Many historical cases of enslavement occurred as a result of breaking the law, becoming indebted, suffering a military defeat, or exploitation for cheaper labor; other forms of slavery were instituted along demographic lines such as race or sex. Slaves may be kept in bondage for life, or for a fixed period of time after which they would be granted freedom.[2] Although slavery is usually involuntary and involves coercion, there are also cases where people voluntarily enter into slavery to pay a debt or earn money due to poverty. In the course of human history, slavery was a typical feature of civilization,[3] and was legal in most societies, but it is now outlawed in most countries of the world, except as a punishment for a crime.