Civil War Era Studies professor Allen Guelzo wrote a September 21 opinion piece for the Wall Street Journal titled "How Lincoln Saved the 'Central Idea' of America."
From the Wall Street Journal:
What the American Revolution began, the Civil War completed. That, at least, was Abraham Lincoln's view of what was at stake in the Civil War, and especially what was at stake in the Emancipation Proclamation he issued on Sept. 22, 1862—150 years ago this weekend.
"I consider the central idea pervading this struggle," Lincoln commented to his secretary, John Hay, in May 1861, "is the necessity that is upon us of proving that popular government is not an absurdity." In other words, as he told a special session of Congress on July 4, the American republic was an "experiment" to see if ordinary people, living as equals before the laws and without any aristocratic grades or ranks in society, really were capable of governing themselves.
One way of falling over into "absurdity," Lincoln knew, was by breaking up a republic whenever any sizable minority of its citizens didn't get their way—as when the Southern states seceded. The other way was when those same people excluded an entire race from self-government.