Civilization under a written language, bronze, full body garment, stone or brick dwelling/fortress & grand cities most likely began In the Caucus region. 4 small empires emerge in the middle east (mesopotamia & egypt). They were the Persians, Assyrians, Hittite, & Egypt with bronze at their disposal. Soon after larger Greek & the Romans empires emerges. East of the Caucus, Oriental empires emerges with iron, cast iron, & steel, later on, at their disposal, then India & Khmer.
Since then slavery has been around, Until N/W Europeans & quakers decided to end it, contemplating of a new age where slavery would no longer be acceptable. Others followed, others needed convincing, & some were forced. In any culture or society it was much a way of life, the practice was a "Display of Superiority involving Nationalistic/Tribal Prejudicial Arrogance" over the spoils who were victims of their own inferiority fated with genocide as were the berbers threatened with genocide through islamic conversion (inquisition) & slavery.
Skin tone, Facial features, technological achievement/prowess, Clothing, Cultural differences & religion were identifiers. All competes with other villages, kingdoms or empire within or along their borders for supremacy. Casoids of different tribal groupings (latins, nords, greek, celts, levant (arabs/hebrews), persian, turks), Empires further east, Amerindians across the Americas, & even sub saharans clashed with those in their region along or within their borders for supremacy.
Ancient belief in the caste system (Ancestral bondage/chattel) still exist in india & africa. Albinos are hunted down for body parts used in medicinal purposes or luck. Warfare, raiding, & lynching still persist in sub sahara. In the Americas, the aztec & mayans cultivate neighboring/surrounding tribes for sacrificial ceremony & view white as godliness (cortez & columbus was thought to be) akin to purity & light that give life (photosynthesis) warmth & happiness while darkness unleashes fear, loneliness, despair, & sadness just as white lions are worshiped in south sub sahara.
The Sahara Desert was a great barrier between the mid eat & sub sahara so societies didn't emerge into a technological civil empire in the likes of Qin, Rome, Greece, Hittite, Persia, Assyria, Summeria, & India. Camels originating from asia enable importation of eastern sub saharan slaves while some were assimilated into middle eastern world of written language, bronze, trade & society to establish arab slave ports, until giant european boats made it quicker than crossing the sahara. W. europeans (portuguese at first, then spaniards, then dutch) with their ship & captain being more efficient in long distant travel establish with certain tribes slave ports. Sub saharan deceases kept slave traders from venturing further inland outside of the trading ports. 10-20 slave traders armed with time consuming inaccurate musket cannot subdue 50-100 spears in unfamiliar tropical decease ridden unfamiliar lands, the winchester repeating riffle or the gatling wasn't available until after the U.S. civil war. The trade involved in american crops but mostly iron-technology (mostly guns), accessories, & appliances that sub saharans could not replicate in exchange.
Kingdom of Bambara (Mali), Benin, Khasso, Bonny, Dahomey grew increasingly rich & highly dependent on the slave trade arguing that the slave trade is the ruling principle of their people, the source & glory of their wealth for it must continue as it is the verdict of their oracle and priests, though western european countries, however great, can never stop a trade ordained by God himself.
They benefited a great deal in trading off their rejects, criminals, & rivals no longer have to deal with their captives, profiting leaving more space, rather than executing thier captives in annual ceremonial custom.
Those brought into a world of written language, Casoid/Asian tech, commerce, economics, mechanics, science, religion (abrahamic) etc. were transformed to learn basic operation of duties. Their transformation led them to abandon & ashamed of their nilothic faiths, custom & culture.
Curious & determined few aided by sympathetic masters & abolitionist acquired knowledge from the Eurocentric society they're in, beyond basic or indigenous sub saharan knowledge earning the friendship of a president. Another researched a means of revitalizing nutrients of depleted fertile lands with crop diversity, & a free descendant by birth who led a team of engineers to develop a gigahertz processor chip, not ground braking but note worthy.
Slavery was a big mistake as it tends to be an "INVASIVE" not to mention that there is less incentive to be productive. The U.S., Caribbean & Brazil, would have been populated more by Amerindians, instead of sub saharan settling through european conquest & marine technology.
Canada, Mexico, Peru, Chile, & Argentina quickly followed Northern Europe to banned importation of sub saharan while slave population was .001% for Canada & 1% for Mexico & others for they anticipated the burden that came with it that is now proving to be a curse. Mexico's nationalistic immigration laws reflects that anticipation. A civil war may not have been fought over a 10-15% slave population. Yet Cuba & brazil had 2- 3x larger population & never went to civil war, although, it took much longer for them to phase it out.