You could go further back and talk about the Romans....
But it was the Dutch who started the slave trade between Africa and the New World.
Over the course of four centuries, beginning in the 1440's, Africa lost more than 10 million people to the Atlantic slave trade. Slavery had existed in Africa and throughout the Mediterranean for centuries before the Portuguese arrived on the West African coast. Primary function of slavery in West Africa was social rather than economic:to provide a place in society for people who where prisoners of war, committed offense, or cut off from the family. Although trans-Saharan traders transported a few Africans for sale to wealthy Europeans, most slaves remained in West Africa. Portugal began growing sugar as early as 1452, on the island of Madeira, off West Africa. To supply Madeira, Portuguese merchants purchased black slaves from Muslim Tran-Saharan traders and from African off the West Coast of Africa.
The earliest slave traders were their own people.called indentured servants .they sold their own children into servitude in order to pay a debt to another or society to stay out of prison/dungeons. All the way back to the beginning of time.(recorded history)