In President Abraham Lincoln's mind, the Civil War began as a war to force the rebellious Southern states back into the Union from which they tried to separate themselves. On January 1, 1863, after almost two years of war, however, Lincoln signed the Emancipation Proclamation, freeing the slaves in the states in rebellion against the Union, and the war became a conflict to end American slavery. If the South won its independence, slavery would remain in place in the rebellious states; if the North won, the rebellious states would be forced back into the Union without slavery.

Abolitionists like Senator Charles Sumner of Massachusetts, Congressman Thaddeus Stevens of Pennsylvania, and Frederick Douglass played a key role in prompting Lincoln to issue the Emancipation Proclamation. During the early part of the war, Douglass's fiery abolitionist editorials in Douglass' Monthly urged the reluctant...