And they were forced to free them. The first Barbary war was to get Africa to stop its slave trade. But they kept at it, and escalated to kidnapping for ransom. So the 2nd Barbary war was fought to force their compliance, and this time Europe stayed in occupation after the war to enforce their compliance.
Largely it just went underground. There are still 15 countries where slavery has not been made illegal, and those are primarily Muslim countries.