First, I have some observations on the trade itself, then suggestions about how to deal with it for the purpose of this assignment.
A Historical Synopsis
The transatlantic slave trade originated in the waning decades of the 15th century. Although the Portuguese were its primary facilitators, many nations, both European and African, were in on the act. Don't be naive. At this period of history, slavery was a common institution across most of the world, where criminals or POWs were routinely condemned to intervals (though not always their whole lives) of hard forced labor. None of the people who instituted the transatlantic trade would have been morally outraged by the concept.
What made the transatlantic slave trade different were its sheer scale, the brutal conditions that slaves had to endure during transport to their places of bondage, and the absolute hopelessness of their situation upon arrival. CONSERVATIVE estimates put the number of people dying during transport across the ocean at about two million. Given the incompleteness of historical records the true figure could be twice as great, and that doesn't even consider people's ugly fates in bondage. The transatlantic slave trade certainly ranks right up there with the Nazi Holocaust and Stalin's Gulag as a MAJOR blot on human history.
If you ever need a case study in which the pursuit of free enterprise and the laws of supply and demand and were not good for society, this is it. The slave trade enriched people on the receiving end in the New World by making difficult agricultural schemes profitable, enriched people on the supply end who gained access to high-end manufactured goods by selling their POWs, and fabulously enriched the middle-men with the ships. Anyone who's grown up in this country knows about the grief and pain resulting from our historic tolerance of slavery, and has, in their personal life, tasted the poison that still flows through our cultural veins as a result. Less is known about the effects of the supply side of the trade, so it's worth a few words.
The transatlantic slave trade began when the Portuguese instituted a simple exchange of manufactured goods (fine pottery, textiles, iron and steel tools, and firearms) for West African forest products (gold, spices, and slaves). With the colonization of the New World, this developed into a triangular system in which manufactured goods were traded for West African slaves, which were, in turn, traded for New World agricultural exports. In time, the Portuguese were joined by the Dutch and English as major protagonists.
Rulers and merchants of the West African city-states visited by the Europeans sought to expand their trade by finding more and better products to trade. Kingdoms like Asante (in the modern Republic of Ghana) that boasted productive gold mines had no trouble attracting the trading ships. Less well endowed kingdoms exported spices, ivory, and their POWs (which were in good supply because these states were often at war with one another.) In principle, this wasn't really different from the export of slaves to the Mediterranean through the Sahelian trading kingdoms that had been going on for centuries. What was different was the scale of the operation.
When India became part of Portugal's trading network, the demand for West African spices declined, leaving many kingdoms with little of value to export except surplus human beings. This coincided with the expansion of slave-based plantation agriculture in the New World, setting in motion a self-catalyzing economic shift in which West African states became increasingly specialized as slave producers. Of course, this gave them an incentive to wage war with their neighbors, simply to "harvest" POWs for export. Increasingly, European traders fed this fire by paying for slaves with firearms.
Although governments and leading citizens got very rich as slave suppliers, the overall societal effects of the slave trade were very bad:
At some point or other, slaves were taken from the entire region from Senegal to Angola, but this activity focused in different places at different times. Senegal, Guinea, Sierra Leone, and Liberia supplied slaves very early in the trade because they were among the first regions contacted by the Portuguese. By the 18th century they had been eclipsed by regions farther south. (In the 19th century, Sierra Leone, and Liberia were actually colonized by freed slaves from the New World.) The gold-exporting Asante, actually TOOK Nigerian and Dahomey slaves from the Europeans in exchange for gold. The major hot-spots of slave export were:
In Angola, the situation was slightly different. There, the Portuguese tried to set up a system of trade with local suppliers similar to that of the "slave coast," however their local trading partners, the kingdoms of Kongo and Ndongo, were more fragile, vulnerable to reprisals, and exerted less control over the countryside, motivating the Portuguese to establish colonies and manage the slave trade themselves. Many early colonists intermarried and assimilated with local populations. Thus, if your ancestors lived in Angola in CE 1800, then probably some of their ancestors lived in Portugal inCE 1490.
During the nineteenth century, democracy and industrialization took root in North America and Europe, and the slave trade started to look both morally repugnant and unprofitable. By 1870, the trade had completely ended. (Even the Confederate Constitution outlawed the international slave trade, but of course they weren't exactly hurting for slave labor.) This spelled economic disaster for the kingdoms that had thrived on slave export. Indeed the civil unrest that this provoked provided the pretext for the next stage of West African misery - European colonialism.
Doing the Assignment
So, if any of your ancestors were transported by the transatlantic slave trade, two things are likely:
But all is not lost: