Slavery was the normal way of running a state/country/city for the vast majority of history. The white/black thing is only a (comparatively) recent variation. The Roman Empire ran off slavery. The Vikings raided to catch slaves, as the most profitable items they could find. The Arab culture was based on slavery - an Arab wreck found recently in the English Channel is thought to have been wrecked during a slave raid. Central American cultures ran on slavery.
Now stopping slavery - that's something else.