The Civil War was fundamentally a conflict over slavery. However, the way Lincoln saw it, emancipation, when it came, would have to be gradual, as the most important thing was to prevent the Southern rebellion from severing the Union permanently in two. But as the Civil War entered its second summer in 1862, thousands of enslaved people had fled Southern plantations to Union lines, and the federal government didn’t have a clear policy on how to deal with them. Emancipation, Lincoln saw, would further undermine the Confederacy while providing the Union with a new source of manpower to crush the rebellion.