The African slave trade was initiated by the Portuguese in the early 15th Century. During this time, Prince Henry the Navigator frequently sent ships to explore the West African coast. These ships sometimes returned with African slaves they had bought or captured as a form of payment for these voyages. Beginning in the 1430s, Portuguese slave voyages to Sub-Saharan West Africa increased as more trade networks in the region were established. This practice was given papal approval in 1455 when Pope Nicholas V granted Portugal the rights to the slave trade as long as all slaves were converted to the Catholic faith. By the second half of the century, Portugal had established itself as the leading slave power of Europe. In fact, any slave ship heading to the west coast of Africa required royal authorization from the Portuguese. Labor shortages in Portugal meant that the nation brought in thousands of African slaves at a time in which they were rare elsewhere in Europe.
By the time new sea routes were being established and the Americas were being explored and conquered, Portugal had already become well-established in the African slave trade. Given the preponderance of slavery among the Portuguese, it should come as little surprise that they brought many slaves to the Americas as they built up their overseas empire in the 1500s. They even handled the bulk of slave importation for the Spanish colonies during the colonial period. The Portuguese were well-positioned to do this because they already had long-established contacts in the slave markets in West Africa and Angola in particular. As a result, Portugal brought more African slaves across the Atlantic than any other European power.