The slavery is something associated with as old as human history. Starting from ancient Mesopotamia (Modern day Iraq), Sumeria (Iraq-Kuwait) to present day Somalia, it was brutally enforced over the underprivileged and marginalized people. The information about slavery, we can find it in the Mesopotamian Code of Hammurabhi (1800 B.C). However, slavery is very rare among hunter-gatherer communities. The wars were the source of slavery . The Byzantine-Ottoman wars, and Ottoman wars with Europeans resulted in the large number of Christian slaves. The Europeans, Arabs and West African Kingdoms played a huge role in the Atlantic Slave Trade.
Nearly 5 to 6 million slaves were sent to Brazil from Africa from 16h century to 19th century (1500 to 1870). In the same period more or less another 4 to 5 million slaves were sent to the United States of America.