The evolving politics of Abraham Lincoln
While personally opposed to the institution of slavery, when elected Abraham Lincoln had no intention of abolishing slavery (he did not believe Congress or the Executive had the constitutional authority to do so). Further, at the start of the Civil War, Lincoln was emphatic that the war was not about the abolition of slavery but simply about re-unification. 
After a couple of years into the war and persistent pressure from abolitionists, Lincoln eventually changed his position and would later refuse to consider any premise of peace talks with the Confederacy without the preconditions of reunification into a single nation and the abolition of slavery.
- Gwynne, S. C. Hymns of the Republic: The Story of The Final Year of The American Civil War. New York: Scribner, 2019.