As Butan said slavery was a universal concept, everyone did it at some point in their history, what was especially bad about the Atlantic slave malarkey was deciding a 'race' was suitable for being slaves, and that's cos it was actually abolished in Europe long before the first explorers reached Africa, and the local chiefs offered them slaves in exchange for various goods the chiefs wanted. This became an industry, and i'm not absolving anyone from guilt, but it wasn't the white men who went to the unprepared villages and snatched people and tied them up, took them across country and loaded them on the ships. The only reason the Atlantic Slave Trade happened was cos it was already a huge industry in Africa at the time, and it was customary to exchange slaves over there. The only difference being where the slaves went after when exchanged to Europeans, across the sea to a different continent, which sounds harsh, but when you consider the size of Africa, if you were captured in Central or Eastern Africa, and sold to someone in West Africa, you may as well be on a different continent; your owners would speak a different language, you'd be in a totally different culture, and climate, and you'd never make your way back home, and that's what the system was anyway long before Europeans rocked up. If anything travel across sea was easier back then than travel across a huge landmass, at least until railways were built in places.
The fun fact is the only reason we don't hear of the horrible lifestyle of slaves before Europeans turned up, is cos slaves only became literate and able to express their struggle to the world once they were taken by Europeans. If you'd read Olaudah Equiano, in his account of his enslavement, he was first sold to a wealthy African household, surrounded by people who dressed differently, spoke differently, ate differently to what he knew (Africa's a big place), he was beaten etc. He was taken on a slave ship, learned to read and write, was freed, became a sailor, saw the world and was a massive influence on the abolition of the slave trade. He became an icon for the freeing of slaves, what exactly would his prospects have been if he'd stayed in the African household as a slave there? The thing is, the more you learn of nearly anything in history the harder it is to just make it about good guys and bad guys, the slave trade is one of those. Say what you will about me, but i know a huuuge amount about the slave trade, so feel justified in using it as a point of reference. I'm being subversive, i know, but the Atlantic Slave Trade is very well taught in schools... apart from the African context, and the circulation of slaves in Africa before European involvement which funnily enough gets sidestepped in the curriculum, once again presumably cos that's the one aspect we don't have to feel bad about, so why bother learning the whole picture?