And between Morrowind and Blackmarsh? Slavery was outlawed by King Hlaalu Helseth, but it sparked civil war. I'm not truly certain the conflict was settled before the Emperor's assassination.

[He had some personal interest in this matter. His own wards had been quite involved in this issue, or at least he suspected as much. No one had ordered Ocheeva and Teinaava to speak on their time spent in service to Argonia, but Shadowscales did not simply guard their king. That would be a waste of their talents. No, they almost certainly would have participated in weakening Dunmer influence at the northern border, killing both slave raider and collaborationist alike.]