I believe that Lincoln's objective was to Centralize the country by usurping power for the federal government to an extent that defied the Constitution, especially the 9th and 10th Amendments. Indeed, this was a direct result of the War at the same time Manifest Destiny got a big push with the westward expansion into Indian Territory. Does not most of the land in the Far Western states belong to the federal government? In Texas, over 98% of the land is privately owned.

Lincoln's true legacy is not "preserving the Union" or freeing anyone. It is centralizing the government with powers that were forbidden by the Constitution. Manifest Destiny in the post War was beneficial towards this goal.