It's important to remember that all civilizations practiced slavery, and not just in the remote past. African tribes cooperated with Arabic slave traders by selling them prisoners from rival tribes. American Indians practiced slavery; so did the Aztecs. The Barbary pirates captured millions of Europeans, at the very same time that other Europeans were enslaving Africans. Mauritania only abolished slavery a decade ago. And so on. Taking a broad view of history, westerners are no more guilty of enslaving other peoples than anyone else.