Abraham Lincoln was a repo man. - Allen C. Guelzo

[E]verything in the reasoning of the founders pointed inexorably toward the incompatibility of liberty and equality with slavery...

[I]n a liberal democracy, sovereignty lies in the people at large; and our governing structures exist to implement that will.

Union (and the liberal democracy it represented) and emancipation were not, after all, mutually exclusive goals. Unless the Union was restored, there would be no practical possibility of emancipation, since the overwhelming majority of American slaves would, in that case, end up living in a foreign country, and beyond the possible grasp of Lincoln's best antislavery intensinos.