Slave trading dominated the Portuguese economy in eighteenthcentury Angola. Slaves were obtained by agents, called pombeiros, who roamed the interior, generally following established routes along rivers. They bought slaves, called peças (pieces), from local chiefs in exchange for commodities such as cloth and wine. The pombeiros returned to Luanda or Benguela with chain gangs of several hundred captives, most of whom were malnourished and in poor condition from the arduous trip on foot. On the coast, they were better fed and readied for their sea crossing. Before embarking, they were baptized en masse by Roman Catholic priests. The Atlantic crossing in the overcrowded, unsanitary vessels lasted from five weeks to two months. Many captives died en route.

During the sixteenth century and most of the seventeenth century, Luanda had been the main slave port of the Portuguese, but toward the end of the 1600s they turned their attention to Benguela. Although the first efforts at inland expansion from Benguela failed, the Portuguese eventually penetrated the Ovimbundu kingdoms and subjected their people to the same treatment that had earlier befallen the Mbundu. By the end of the eighteenth century, Benguela rivaled Luanda as a slave port.

According to historian C.R. Boxer, African slaves were more valued in the Americas than were American Indian slaves because Africans tended to adjust more easily to slavery and because they were less vulnerable to the diseases of the white man. Boxer also suggests that Jesuits in the New World opposed the notion of using Indians as slaves, whereas they were less resistant to the use of Africans as slaves. Many of these African slaves were sent to Spanish colonies, where they brought a higher price than they would have if sold in Brazil.

From the late sixteenth century until 1836, when Portugal abolished slave trafficking, Angola may have been the source of as many as 2 million slaves for the New World. More than half of these went to Brazil, nearly a third to the Caribbean, and from 10 to 15 percent to the Río de la Plata area on the southeastern coast of South America. Considering the number of slaves that actually arrived, and taking into account those who died crossing the Atlantic or during transport from the interior to the coast for shipping, the Angola area may have lost as many as 4 million people as a result of the slave trade.

By the end of the eighteenth century, it became clear that Lisbon's dream of establishing a trading monopoly in its colonies had not been achieved. Competition from foreign powers contributed significantly to Portugal's inability to control the slave trade, either in Angola's interior or on the coast. In 1784, for example, the French expelled a garrison that the Portuguese had established a year earlier in Cabinda. Portugal was also concerned about the northward expansion of Dutch settlers from the Cape of Good Hope area. Moreover, at this time the British, Dutch, and Brazilians, not the Portuguese, were contributing most of the capital and vessels used in the slave trade. Furthermore, many of the European goods arriving at Angolan ports were coming from nations other than Portugal.

Data as of February 1989