The nation as we know it would not actually BE a nation if it had not been for the action of enslaved and freed Africans during the Civil War. The Fourteenth Amendment besides giving citizenship to black men and women, actually created the "national citizen." Before the passage of the 14th, one was a United States citizen through being a citizen of a given state. Afterwards? The nation came first and foremost.
But few have considered the Corwin Amendment. I've begun to think about an alternate timeline beginning with the passage of the Corwin Amendment.