Slavery was not a stagnant institution in the United States in the period between the Revolution and the Civil War, it spread in some areas while disappearing or constricting in others. Slavery was perhaps the most volatile issue facing the new nation. One the eve of the Civil War, there were 19 free states and 15 slave states, eleven of which would come together as the Confederacy. This interactive map from A Biography of America traces the legal status of slavery in states and territories of United States from 1776 to 1865.