It is closest to Germany or Italy in that it is a Federation consisting of one nation. The US united different polities that were not different nations. In some ways, it is one "nation-state" in that a nation-state is a concept that seeks to draw boundaries based loosely upon ethnicities. In a way, that was partially Hitler's justification -- in his mind the Austrians, Czechs, Norweigans, and English were all "German," and should be united into one state.
It is not a federation of different nations like the Russian Federation. In Russia, the Tatars are not the Bashkirs, and the Finns are not the Mari-El, and none of them are "Russians." They have their own Republics under umbrella of the Federation. That's not the United States.
The real debate that was underway was are the states "independent?" I don't know that they ever really were. The "EU" argument creates a historical fiction that justifies a certain point of view. As was pointed out, the Northern textile mills made plenty of money off of cotton grown in the South. It would be foolish to think that the North and South could ever really exist without the other.