My Old view (pre ~1998?): Slavery was a white-on-black injustice created by Europeans, and which devastated an otherwise just and civil African continent.
My New view (post ~1998?): Slavery was a widespread social practice, just as popular as black-on-black forms in Africa as it as white-on-white forms in Europe. In the 1500s - 1700s, all human civilizations to that point comprised all manner of evil and awful practices, with the rule of might dominating: people organize and take from each other whatever their armory and deviousness could earn them. In this regard, no people of any "race" or on any continent were any better or worse than any other. During different periods of time, different groups of people led the way in advancing civilization in its various forms: architecture, law/justice, literature, science, math, etc.
History shows that both African leaders such as Shaka Zulu as well as various European rulers have visited the absolute worst possible crimes of social conquest on other people bearing their same skin color. Unless you and I were born into royal positions in either sort of society, we would both find ourselves living under crushing everyday injustices.
People in the US today who call themselves "white" or "black" both have ancestors who were slavers and slaves, rapists and rape victims, thieves and the victims of thieves, cultural suppressors and cultural suppression victims. White people in history have done all this to each other, and so have black Africans. At some point these different groups of people started taking slaves from each other's continents. White people started buying from black slave traders who had captured black slaves. The lives of black slaves owned by blacks in Africa was no less horrible than blacks owned by whites as slaves in the Americas, though of course making the middle passage was a special horror. Black slavers in Africa even took several million white slaves, captured by Barbary ships on the north African coast, a practice that led Tom Jefferson to form the US marines and begin the US' first foreign war.
When white folks started the Anti-Slavery Society in London, their opponents included not only evil honkey bastards, but also many African leaders as well. In fact, black-on-black slavery in many African nations did not end until the 1900s, and in some places has not even yet ended today. The freed US black slaves who created Liberia created black-on-black slavery in their ironically named new nation, calling themselves "Americans" and the natives "Africans". These slave owners imposed Christianity on the "Africans", as well as English. Something similar occurred at the conclusion of Haiti's revolution.
Your kids and mine have black and white ancestors. On both sides they have victims of slavery and brutal cultural conquest, as well as perpetrators of same. Different societies over time have been better or worse than their contemporaries. For our children today, I think that immigration statistics show that we should keep them put: many thousands of black Africans immigrate here to the US, and nearly no Americans immigrate to anywhere in Africa.