Lincoln saw the war in its global dimensions. . . As Lincoln saw it, the Confederate states had rejected two fundamental precepts of democracy. First, in refusing to accept him as their President and making his election their justification for withdrawing from the Union, they had violated the first rule of democratic government, the obligation of a minority to abide by the result of an election. . .
Second, in making slavery the foundation stone of their new government, the Confederacy was renouncing the doctrine of the equal rights of man in favor of the creed of the master race, an idea that Lincoln abhorred. . . .
When we realize that Lincoln saw the dissolution of the Union as a threat to democratic aspirations throughout the world, his words at Gettysburg become more meaningful. Chancellorsville, Antietam, Chickamauga and Gettysburg were deciding more than the fate of these United States. Americans were dying for the new, revolutionary idea of the free man, even as they had died at Bunker Hill and Yorktown. They were dying to save the hopes of all people everywhere.
To counter that line of thought, here's H L Mencken on Lincoln's brief speech:
Like William Jennings Bryan, he was a dark horse made suddenly formidable by fortunate rhetoric. The Douglas debate launched him, and the Cooper Union Speech got him the Presidency. His talent for emotional utterance was an accomplishment of late growth. His early speeches were mere empty fire-works—the hollow rodomontades of the era. But in the middle life he purged his style of ornament and it became almost badly simple — and it is for that simplicity that he is remembered today. The Gettysburg speech is at once the shortest and the most famous oration in American history. Put beside it, all the whoopings of the Websters, Sumners and Everetts seem gaudy and silly It is eloquence brought to a pellucid and almost gem-like perfection—the highest emotion reduced to a few poetical phrases. Nothing else precisely like it is to be found in the whole range of oratory. Lincoln himself never even remotely approached it. It is genuinely stupendous.
But let us not forget that it is poetry, not logic; beauty, not sense. Think of the argument in it. Put it into the cold words of everyday, the doctrine is simply this: that the Union soldiers who died at Gettysburg sacrificed their lives to the cause of self-determination — "that government of the people, by the people, for the people," should not perish from the earth. It is difficult to imagine anything more untrue. The Union soldiers in that battle actually fought against self-determination; it was the Confederates who fought for the right of their people to govern themselves. What was the practical effect of the battle of Gettysburg? What else than the destruction of the old sovereignty of the States, i.e., of the people of the States? The Confederates went into battle free; they came out with their freedom subject to the supervision and veto of the rest of the country — and for nearly twenty years that veto was so effective that they enjoyed scarcely more liberty, in the political sense, than so many convicts in the penitentiary.
I would argue further that Lincoln's use of the words "nation" and "national" excluded the Southern states, or at least, the great majority of white people in the South.