The defeat of the Confederacy and the establishment of military rule by the union army in the south was a triumph for a particular interpretation of the United States Constitution; after the Civil War relations between the states, I think, lose the character of diplomatic relations between countries which they had often had. It's often said that it was only after the Civil War that the idea of the United States as a singular entity overcame that of it as a collective - "this United States" replacing "these United States" but I'm not sure how true that really is.