Slavery was found in the history of most civilizations. Slavery flourishes where there is a high demand for labor and not enough workers. When the workers are plentiful, slavery dies out because it is unprofitable. That is, it becomes cheaper to free a slave and hire low cost paid labor than to buy and maintain slaves. Typically, when it had almost died out, it was made illegal by the government, as in Brazil.
The most famous insance of slavery was in the American South until it was forcibly ended during the [[American Civil War]] (1861-65)--the only major war in world history involving fought over slavery.
==Economics==
The two main forms of slavery are house servants (in which slaves are luxury items owned by the rish), and field work, in which slaves are used as a cheap labor force. If free labor is cheaper than expensive slaves, slavery will disappear. If there is a shortage of laborers (and an abundance of work to do), slavery becomes economically possible. It is especially profitable in new lands with few people and rich soils or mines that require imported labor.