As West Africa was connected to Europe and Asia by overland and now sea routes, the local population had been exposed to Old World pathogens and fared much better. Between 1550 and 1650, 650,000 Africans were trafficked to Spain and Portugal’s American colonies—more than twice the number of Europeans who crossed the Atlantic in that period.
The explanation provided here seems sound as the indigenous populations, the ideal candidates for forced labor, had been killed off by disease. Given that West Africans had previous contact with Europenas, they were accustomed to the diseases associated with them. Since their immune systems could fight off diseases more readily, they would live longer and thereby offer Europenas a more reliable work foce.
