Historians estimate that between 650 AD and the 1960s, 10 to 18 million people were enslaved by the Arab world. They were taken from Europe, Asia and Africa across the Red Sea, Indian Ocean, and the Sahara desert. For four centuries, beginning in the late 15th century, millions of Africans were taken as slaves by Europeans. They got this idea from the Arab empires which had been taking black slaves from Africa since the 7th century. Europeans began exporting Africans to the New World as a source of cheap labor on colonial plantations. This was called the Atlantic slave trade. Early attempts to enslave Native Americans failed which gave rise to the African slave trade. Africans were a relatively easy source of slaves as European traders did not have to capture them, but relied on Arabs and other Africans to do it for them. Even before outside slave traders took advantage of Africans, the Africans themselves had established slave trading. Theirs was not an economy based on money, but on trading. Slaves were a commodity (a substitute for money).