I know as fully as one can know the opinions of others, that some of the commanders of our armies in the field who have given us our most important successes, believe the emancipation policy, and the use of colored troops, constitute the heaviest blow yet dealt to the rebellion; and that, at least one of those important successes, could not have been achieved when it was, but for the aid of black soldiers. Among the commanders holding these views are some who have never had any affinity with what is called abolitionism, or with republican party politics; but who hold them purely as military opinions. I submit these opinions as being entitled to some weight against the objections, often urged, that emancipation, and arming the blacks, are unwise as military measures, and were not adopted, as such, in good faith.
Letter to James C. Conkling (1863)
President Lincoln wrote this letter from August 26, 1863 to his friend James Conkling, and it is read at a rally in Springfield, Illinois, supporting the Union. In this letter, the President vigorously defends his Emancipation Proclamation. The Collected Works of Abraham Lincoln, vol. 6 (New Brunswick, N.J.: Rutgers University Press, 1953), p. 407-410.