As Enlightenment principles took root in Europe, larger and larger numbers of people grew outraged at the idea of slavery. Between 1807 and 1820, most European nations abolished the slave trade, although slavery itself was not abolished until a few decades later. In other words, no new slaves were legally imported from Africa, but those already in Europe or the New World continued to be enslaved until emancipation in the mid-nineteenth century. In some cases, former slaves returned to Africa. Groups of former American slaves, for example, emigrated to Liberia, where they established an independent nation.
It's a terrible irony that as the slave trade ended in the nineteenth century, Europeans turned their greedy eyes to the continent of Africa itself. Within 50 years, the Africans were subjugated again, but this time in their own homeland.