It is common knowledge that the Trans Atlantic Slave Trade ( ~1500-1800s) sparked the abolitionist movement we are most familiar with, but I am curious about any anti-slavery sentiment earlier than this and what form it took? I found references to anti slavery sermons by Wulfstan of Worcester (1008-10 to 1095 AD). Was there anti-slavery sentiment earlier than this? What about in other areas of the world?
More can be said, but here is a post by a now deleted user discussing opposition to slavery in ancient Rome Were any Roman citizens against slavery in Classical Antiquity?. Additionally we have In the Roman Empire, was there ever any significant debate about the moral issues with slavery? written by u/colorfulpony. Finally, you might be interested in Anti-Slavery in ancient civilizations written by u/Trevor_Culley