Slavery as an institution is not only as ancient as civilization but has been accepted by most societies through much of history. In the United States it was abolished in 1865, in Brazil in 1888, and in Saudi Arabia in 1962. Curiously in Sierra Leone, a country that was established as a haven for freed slaves, the colonial authorities only got around to doing so in 1896. 

Nowhere has slavery been more prevalent than in Sub-Saharan Africa. In the Sahara-Sahel trade there were individuals who owned up to a thousand slaves. Estimates of the incidence of slavery in Sub-Saharan Africa before the 15th century vary from 30% to 60% of the entire population. People could becomes slaves through wars, nomadic raids, kidnappings, sale by relatives, convictions, or simply by straying out of their tribal territory.  

This is not to say that Africans were willing slaves or that the African Atlantic slave trade can be justified because slavery was so common in Africa. The questions are why Africa, the home of mankind, did not develop to a social condition where it could mitigate the internal omnipresence of slavery and why there was nothing in the way of political institutions that could rise in opposition to Europeans and their economic designs. 

The isolated continent

Sub-Saharan Africa used to be called the dark continent. It is probably more accurate to call it the isolated continent, almost as isolated as was the western hemisphere from events in the rest of the world until the arrival of Europeans. The isolation of sub-Saharan Africa was not only from the cultures that lay to the north of the Sahara but also of its peoples from each other. The rise of civilizations is invariably associated with population density. This alone does not trigger the civilizing process, for otherwise the Levant, where agriculture began, would have engendered literacy and city-states before Sumeria. However, the concept of density is broader than its demographic use. There are densities of other sorts. The survival and the advances of civilizations depend upon different "cultural densities".  

On a primary demographic level, Sub-Saharan Africa was lightly populated when Europeans started visiting its coasts. There were no cities anywhere. The enclosure at Great Zimbabwe and its surrounding area cannot have contained more than 20,000 inhabitants, but this is the exception that proves the rule. Even after the arrival of Europeans, the fillip to state-formation did not involve the growth of urban centers.  

Sub-Saharan Africa was a land of villages and these villages were in contact with contiguous villages but not much beyond these. The proto-kingdoms that existed might have involved a royal compound from which at most rule was exerted over congeries of villages and some additional territories such as, for instance, the gold mines of Asante. Additionally, these villages did not thrive everywhere. Much of Africa was thick tropical jungle, uninhabitable desert, or dry, scrubby flatland good only for hunting, collecting, or scavenging. Savannah land, lying between jungle and desert and subject to fickle weather patterns, was considered prime real estate. The Arabs, who for centuries had been sailing down the eastern coast of Africa, did not make any significant urban foundations before the 16th century. Sub-Saharan Africa was pristine, awesome, even sublimely beautiful, but it was not propitious for the development of higher cultures. 

The endemias

And behind the immediate façade there lurked and had lurked since the beginning of human settlement, the scourge of endemic diseases that wasted away those it spared. The habitat of the Tsetse fly in Africa delimits the areas where cattle-raising is possible. This insect affects humans and cattle by injecting a micro-organism called trypanosome, which produces sleeping sickness, a disease that still affects the inhabitants of ten million square kilometers of tropical Africa. Bilharzia and hookworm infiltrate human organs and produce lifelong physical debility. Some one has suggested only mildly in jest that the power of the Pharaohs rested on a bilharzia-infected peasantry capable only of spurts of energy during very brief lifespans. Even some Pharaohs' mummies have been found to contain the bilharzia parasite.  

The greatest of all killers was a lethal form of malaria--other varieties were recurrent and prostrating--for which Africans developed a defense in the form of blood corpuscles called sickle cells. The problem with this adaptation is that when sickle-cell genes are inherited from both parents it produces an anemic sickness which is usually fatal. Caught in the reciprocally reinforcing traps of difficult environments, enervating climates, and killing or wasting diseases, the population of Sub-Saharan Africa did not grow very much. Overall population estimates for the Americas in the 15th century are even lower than those for Africa, but they were as high as those in Europe in the heartlands of the Aztec and the Inca empires.

Isolated from cultural diffusion from the north by immense desert wastes, African populations by themselves never attained the concentration needed for the cultural density that would have produced more evolved political formations. As would be expected, the arrival of Europeans for the sole purpose of economic exploitation not only did not raise the cultural level at which Sub-Saharan Africa was but it exacerbated the social conditions that made slavery a virtual universal institution. 

Atlantic slave trade

The Spaniards might have had their doubts about Columbus' project, but they also knew how far the Portuguese were advancing in their explorations and they wanted to share in the riches of India. They were in a position to know because in compensation for an undue Portuguese interference in the succession of Isabella, Portugal had ceded the Canary Islands to Castile. Columbus obtained the sponsorship he was looking for and on 12 October 1492 discovered what he thought was India, or at least, the approaches to it. He and the Spaniards must have been disappointed at not finding spices and gold, but they had to make do with what they had at hand. They would soon discover much more but for the moment they began planting sugar in La Hispaniola and in 1510 the first shipment of African slaves was sent to America. This was but the trickle of a torrent of which we can only do a brief summary here. 

Truly reliable statistics about the Atlantic slave trade are hard to come by. But the general lines are known and there are some hard facts. In the late 18th century the infamous slave-transporting ship Brookes was built in Liverpool to specifications. Its hold was partitioned into spaces no larger than a coffin in order to permit it to hold as many slaves as possible. Not one inch of carrying capacity was lost and even so on occasions the ship transported 600 slaves, which was more than it was designed to accommodate. The slave trade thrived on a triangle which had manufactured goods at a vertex (Europe or New England), African slaves at another, and West Indian sugar and rum at the third.  

Gold was initially used to purchase slaves. Each slave was paid with one ounce gold. These rates, of course, would change over time. Copper was much prized in Africa and copper goods, especially bracelets, soon became the principal means of exchange. The most amazing "currency" used by slave traders were cowrie shells. These had been used before in Africa, but the Portuguese fomented their massive circulation. Cowrie shells are small, spotlessly white, and shiny. They reproduced in limitless abundance in the Maldives. Initially the going price for one slave were 6,370 cowries. By the 1770s, although there were more slaves than ever on the market, the price had risen to 170,000 cowrie shells per slave.  

How such an intrinsically worthless object could actually have been accepted as currency is one of the rational inconsistencies of African history. However, the slave trade normally also involved textiles and metal wares of all sorts. Guns were much appreciated. The total of exports to Sub-Saharan Africa from 1500 to 1900 is estimated at 20,000,000, which sounds as if the Europeans were weaponing Africans, but the average is only about 50,000 a year, which spread over a coastline of thousands of kilometers (from Senegal to Angola) was hardly enough to arm companies of men here and there. In any event, guns were not turned against their suppliers, but used for more slave-raiding. 

Estimates

Estimates of slaves bought and transported by Europeans from the first such venture in 1451 to 1900 vary from as low as nine million to as high as thirteen. From 10% to 20% of the total died en route from their origins to their destinations. The height of the slave trade was during the 18th century when an estimate of average annual transportations is of around 60,000.  Some calculations give grounds for caution. One estimate is that 42% of slaves ended up in the Caribbean basin. Using a median figure, four and a half million Africans would have been transported to the Caribbean. Assuming that most arrived before the mid-19th century, a natural rate of reproduction over two centuries would give figures such that are not likely from present-day population figures and the ethnical composition of that region. The African-descended population of Brazil is larger than that of the Caribbean basin and the Gulf of Mexico.  

The slave trade was prohibited by Great Britain in 1807 and by the United States the following year. It was the British navy that enforced it along the coast of Africa. Nevertheless, one estimate is that 28% of the total Atlantic slave trade occurred during the 19th century. Humane societies in Britain and the United States were responsible for the creation of the freed-slave homelands of Sierra Leone (1787) and Liberia (1821). These two states have in recent times collapsed into civil wars during which mutilations were common practice and children were recruited by force, sometimes ordered to kill their own relatives, and sent to fight in battles as if they were adults, the way the Mongols used captives as a shield against the captives' own resisting peoples. Slavery was the total or partial basis of many local economies in the Western Hemisphere. One sovereign nation at least, the Confederate States of America, was solely created for the defense of the institution of slavery.  

Evidently, it had to be Africa itself that was most affected by the slave trade. The latter's effects were being felt long after it was illegalized. The slave trade propitiated the creation or consolidation of slaver or slaving states, among which Dahomey acquired special notoriety for its habit of enslaving its own people. But Benin, Oyo, Hausa, Bambara, Akwamu, Fulani, Songhai, and Buganda were also kingdoms or proto-states affected by the slave trade.  

Most of these names are properly designations of politically hegemonic peoples, tribes, or clans in vaguely delimited regions. Some African states were powerful enough to absorb neighboring hegemonies, such as Kanem which annexed Bornu. The oldest of these proto-states, Oyo and Benin, can be traced back to the 12th century through various means except chronicles and dynastic successions.  

The Portuguese actually tried to form the kingdom of Kongo with a people of northern Angola (15th century). It had a court which dressed in European style. When slave trading began in earnest, the king of Kongo wrote to the king of Portugal about the conduct of his subjects and the Portuguese monarch replied that his African colleague had no cause for complaint since slaves were the only thing that his kingdom had to export. Some African kingdoms subsisted during the 19th century, but they were all colonialized during the Scramble for Africa (after 1870).  

Slaving was not necessarily a collective enterprise. It was also carried on by individuals, basically part-time kidnappers who sold to large African suppliers lots of five or less fellow human beings. The interdiction by Britain of the African Atlantic slave trade actually increased the proportion of slaves in Sub-Saharan Africa because slavers were left with unsold stock or inventory in their hands. This was partially offset in eastern Africa where the slave trade, involving, according to some calculation, 1,600,000 persons, was directed towards Arabia and the Middle East, another figure which gives ground for caution. In Sub-Saharan Africa estimates are that up to 50% of the population of the Sahel was composed of slaves. Towards the end of the 19th century the kingdom of Sokoto in northern Nigeria, which had annexed the Hausa, had an estimated 2,500,000 slaves out of a population of 10 million. 

Despite the slave trade, the population of Africa grew from an estimated 46 million in 1500 to over 100 million in 1900. Because of low population densities slaving necessarily had different areas of concentration and, according to John Reader, the average African villager was less likely to be enslaved than the average American today to die from a car accident. Nevertheless, slaving in Africa had an over-all brutalizing impact with repercussions to this day. The alternatives for Africa without the incidence of the slave trade are purely conjectural. One certain thing is that few African-Americans would trade their station in life today to that of the vast majority of the population of Africa.