During the Enlightenment, slavery and the slave trade began to be questioned. Many Christians were also influenced by the new ideas. A new Christian ethic slowly emerged. What is right and wrong is not carved in stone.
But it takes time to change established beliefs. In 1833, when the London Parliament voted to abolish slavery in the British colonies, the Bench of Bishops voted against the proposal.
In 2006, the Church of England apologized for the fact that their priests had been owners of slave plantations in the Caribbean.
https://www.theguardian.com/uk/2006/feb/09/religion.world
http://www.badnewsaboutchristianity.com/gaa_slavery.htm
