Antietam was not really a Union victory. It was followed by the retirement of Lee into Virginia, but it is certain that such retirement had been intended by him from the beginning--was indeed his objective. The objective of McClellan was, or should have been, the destruction of the Confederate army, and this was not achieved. Yet, as marking the end of the Southern commander's undoubted failure in Maryland, it offered enough of the appearance of a victory to justify in Lincoln's judgment an executive act upon which he had determined some months earlier, but which he thought would have a better effect coming after a military success than in time of military weakness and peril.
We have seen that both the President and Congress had been careful to insist that the war was not undertaken on behalf of the Negroes. Yet the events of the war had forced the problem of the Negro into prominence. Fugitive slaves from the rebel States took refuge with the Union armies, and the question of what should be done with them was forced on the Government. Lincoln knew that in this matter he must move with the utmost caution. When in the early days of the war, Frémont, who had been appointed to military commander in Missouri, where he showed an utter unfitness, both intellectual and moral, for his place, proclaimed on his own responsibility the emancipation of the slaves of "disloyal" owners, his headstrong vanity would probably have thrown both Missouri and Kentucky into the arms of the Confederacy if the President had not promptly disavowed him. Later he disavowed a similar proclamation by General Hunter. When a deputation of ministers of religion from Chicago urged on him the desirability of immediate action against Slavery, he met them with a reply the opening passage of which is one of the world's masterpieces of irony. When Horace Greeley backed the same appeal with his "Prayer of Twenty Millions," Lincoln in a brief letter summarized his policy with his usual lucidity and force.
"My paramount object in this struggle is to save the Union, and is not either to save or to destroy Slavery. If I could save the Union without freeing any slaves, I would do it; and if I could save it by freeing some and leaving others alone, I would also do that. What I do about Slavery and the coloured race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union."