Even so, Christianity from its very beginning discouraged the enslavement of fellow Christians. We read in one of Paul’s letters that Paul himself interceded with a master named Philemon on behalf of his runaway slave. “Perhaps this is the reason he was separated from you for a while,” Paul says, “so that you might have him back forever, no longer as a slave, but as a brother.” How can a slave also be a brother? Christians began to see the situation as untenable. Slavery, the foundation of Greek and Roman civilization, withered throughout medieval Christendom and was replaced by serfdom, which was not the same thing. While slaves were “human tools,” serfs were human beings who had rights of marriage, contract, and property ownership that were legally enforceable. Medieval feudalism was based on a hierarchical system of reciprocal rights and duties between lords and serfs.

Moreover, Christians were the first group in history to start an antislavery movement. The movement started in late eighteenth-century Britain, spread to other parts of Europe, and then gathered force in the United States, where the economy of the South was heavily dependent on slave labor. In England, William Wilberforce spearheaded a campaign that began with almost no support and was driven entirely by his Christian convictions—a story effectively told in the film Amazing Grace. Eventually Wilberforce triumphed, and in 1833 slavery was outlawed in Britain. Pressed by religious groups at home, England then took the lead in repressing the slave trade abroad.

The debate over slavery in America was essentially a religious debate. All sides claimed the authority of the Bible and the Christian tradition. The slaveowners invoked Paul and pointed to the fact that slavery had existed in Christian countries since the time of Christ. Free blacks who agitated for the emancipation of their fellow blacks invoked the narrative of liberation in the Book of Exodus, in which Moses led the captive Israelites to freedom: “Go down, Moses, way down to Egypt land and tell old Pharaoh, let my people go.”

It’s not entirely surprising that a group would oppose slavery for its own members. Throughout history people have opposed slavery for themselves but have been perfectly happy to enslave others. Indeed there were several thousand black slaveowners in the American South. What is remarkable is for a group to oppose slavery in principle. TheQuakers were the first people in America to oppose slavery, and the evangelical Christians soon followed. These groups gave a political interpretation to the biblical notion that all are equal in the eyes of God. From this spiritual truth they derived a political proposition: because human beings are equal in God’s sight, no man has the right to rule another without his consent. This doctrine is the moral root of both abolitionism and democracy.

The great sweep of American history can be understood as a struggle to realize this Christian principle. For those who think of American history in largely secular terms, it may come as news that the greatest events of our history were preceded by massive religious revivals. The First Great Awakening, a Christian revival that swept the country in the mid-eighteenth century, created the moral foundation of the American Revolution. The revival emphasized that people should not merely know about Christ, but that they should also develop a personal relationship with him. The leading figures here were George Whitefield, the Oxford-educated clergyman who led the newly founded Methodist movement, and Jonathan Edwards, the Yale-educated Congregationalist minister who was president of Princeton University. Historian Paul Johnson writes that the American Revolution is “inconceivable … without this religious background.”