James M. McPherson, "Lincoln, Abraham," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00631.html.
Scorned and ridiculed by many critics during his presidency, Lincoln became a martyr and almost a saint after his death. His words and deeds lived after him and will be revered as long as there is a United States. Indeed, it seems quite likely that without his determined leadership the United States would have ceased to exist. Union victory in the Civil War resolved two fundamental, festering problems that had been left unresolved by the Revolution of 1776 and the Constitution of 1789: whether this republic, "conceived in Liberty, and dedicated to the proposition that all men are created equal," would "long endure" or "perish from the earth"; and whether the "monstrous injustice" of slavery would continue to mock those ideals of liberty. The republic endured, and slavery perished. That is Lincoln's legacy.