the golden circle idea a couple pages back would probably be best to go with. The Plains are more for nomads than kingdoms, without modern infrastructure and technology most of America isnt suited to sedimentary civilisation, the winters and summers too baren, continents make seasons extreme, coasts and mountains moderate and America is on the whole big and flat in the middle. The Rivers and the Coasts and the land near them. Plains being where Mongols, Huns and the other barbarians come from, not civilisation as you need to move with the seasons if youre to live through them.
And the mispronounced or spelt words should be avoided as thats the kind of joke which only stands to make the setting a joke also, look to the Fallout setting and how great they suffer from it.
and why kingdoms and duchies? its not europe, its republic and governor and what have you that are written everywhere, that are remembered. having kingdoms and duchies doesnt really make sense, it implies an arrogance. Hereditary Rule came to europe from the beaucracy of Rome, appointed titles became hereditary when there was no longer anyone to replace them, Dukes born from Dux.
Governorships and Mayoralties handed from father to son to secure stability. Not the stupid and powerful declaring themselves dukes out of vanity and overthrowing the establishment as that would never sustain and not be universal, but the system remolding around the new realities. The same job continuing under the same name and more or less the same function, just differently appointed. Presidents instead of Emperors as the office of Great Secular political Authority, leader of the world, would not be made from memories of Rome but memories of America. Dukes hold no power or authority in america, why should they suddenly gain it when the world burns? The people would turn to existing authorities for leadership and help, as they always do. And when the incumbent died, well his son was always at his side wasnt he? watching and learning, he will know what to do. That's how hereditary rule develops, not from declaration and a romantic view of another continents history, but a slow progression and the need for stability.
If its going to be interesting then the Why and the How of the shape of the world should matter more that the gimmicks and the grandeur. Dont make it a pale imitation of medieval europe but rather a bright and wonderful thing itself which is wholely and entirely itself. If its post-apocalyptic america have it post-apocalyptic america not post-apocalyptic fake-europe. There should always be a reason.
