Almost from the very beginning of the Civil War, the federal government had to start making policy and they said, ‘Well, we’re going to treat these people as free. We’re not going to send them back into the slave holding regions. And the Army opened itself up to the enlistment of black men. And by the end of the Civil War, 200,000 black men have served in the Union Army and Navy. And envisioning blacks as soldiers is a very, very different idea of their future role in American society. It’s the black soldiers and their role which really begins as the stimulus in Lincoln’s change [with regard to] racial attitudes and attitudes towards America as an inter-racial society in the last two years of his life.
Historian Eric Foner, talking about the importance of African-American soldiers joining the Union Army and then changing Abraham Lincoln’s thoughts on slavery, during an interview with Terry Gross, October 11, 2010.