Protestantism is a loose term given to all those who sought to reform and eventually break from the Catholic Church during the Reformation. The movement soon splintered and several denominations arose. By Abraham Lincoln's time, the most prominent Protestant denominations in the United States were Episcopalians, Presbyterians, Methodists, and the Baptists.

Mark A. Noll, A History of Christianity in the United States and Canada (Grand Rapids, MI: W. Eerdmans, 1992); Alec Ryrie, Protestants: The Faith that Made the Modern World (New York: Penguin, 2018).