The four years of Civil War that ripped apart the nation from 1861–65 achieved what seventy-five years of compromise could not: it resolved once and for all the question of slavery in the United States. By 1860, there were 4.5 million slaves in the United States. Military necessity and the force of human passion for liberty pushed emancipation to the top of the nation's agenda. Two major milestones marked slavery's final destruction during the war years: the Emancipation Proclamation and the Thirteenth Amendment to the Constitution.

President Abraham Lincoln issued the Emancipation Proclamation on January 1, 1863, declaring that "all persons held as slaves" within the rebellious areas "are and henceforward shall be free." It also announced the acceptance of former slaves into the Union's armed forces. The Constitution grants extended powers to the President during times of war, and although it would not permit the President to interfere with slavery in the states under normal circumstances, it would do so during wartime.

President Lincoln feared that the Emancipation Proclamation would be overturned once the war ended. A constitutional amendment would ensure that slavery could never again resurface. Congress formally proposed the Thirteenth Amendment outlawing slavery on January 31, 1865; it was ratified on December 6, 1865.