Abraham Lincoln feared that if he pushed too aggressively to end slavery he would lose popular support for the Union cause. But many Republicans in Congress were urging him to take a stand for freedom. In 1862, under his authority as commander in chief, Lincoln drafted and issued the Emancipation Proclamation, ordering that on January 1, 1863, all slaves in states still in rebellion would be "then, thenceforward, and forever free." The abolition of slavery was now an aim of the Civil War and, with Union victory, a virtual certainty.
The proclamation's constitutionality was questionable, and the Republican Party dedicated itself to changing this. By the end of 1865, the nation had ratified the Thirteenth Amendment, outlawing slavery in the United States.