Christianity Against Slavery

It didn't start with William Wilberforce.  As far back as Augustine the church has sought to free those caught in slavery.  I saw this over at Euangelion where Michael Bird quotes a piece from Augustine's Letter to Alypius (#10, ca 428 AD):

Even the examples of this outrage that I have personally encountered are too many for me to list, if I wished to do so. Let me give you just one example, and you can estimate from it the total extent of their activity throughout Africa and along its coasts. About four months before I wrote this letter, a crowd of people collected from different regions, but particularly from Numidia, were brought here by Galatian merchants to be transported from the shores of Hippo (It is only, or at least mainly, the Galatians who are so eager to engage in this form of commerce). However, a faithful Christian was at hand, who was aware of our practice of performing acts of mercy in such cases; and he brought the news to the church. Immediately, about 120 people were set free by us (though I was absent at the time), some from the ship which they had to board, others from a place where they had been hidden before being put on board. We discovered that barely five or six of these had been sold by their parents. On hearing about the misfortunes that had led the rest of them to the Galatians, via their abductors and kidnappers, hardly one of us could restrain their tears.

Bird goes on to ask, "So what did you do after church last Sunday?"