Conquered peoples -- often referred to as barbarians -- and persons imprisoned for debt were used as slaves by the Babylonians, the Egyptians, the Greeks, the Persians and the Romans.
The Middle Ages saw the advent of the Saharian, Nilotic and Great Lakes network of Arab routes for the draining of slaves from the heart of Africa.
The discovery of the Americas by westerners marked the advent of a black slave trade on a vast scale. The Spanish and Portuguese, who divided the New World between them after 1493, desired to exploit these lands. However, the populations of some regions, particularly the Greater Antilles, were decimated by war, disease imported from Europe and sheer ill-treatment. And the exploitation of American land and gold and silver mines would call for large numbers of robust and, if possible, cheap labour. Las Casas, disturbed by the treatment given to the Indians, had the idea of using Africans whom he considered were of sterner stuff.
Over the next hundred years the English joined the race for the American colonies, followed by most of the nations of Europe including Denmark, France and the Netherlands. Colbert sought to control slavery when he drew up the first Code Noir in 1685, thus making slavery official. Thus the slavery involving the Indian communities, and later the black populations, was of a quite different kind.
Black slavery, known as the triangular trade, developed at lightning pace. Men, women and children were captured and sold. The various waves of slavery resulted in the deportation of an estimated 25 to 30 million persons, not counting those who died on board ship or in the course of wars and raids.