The History Of Westfall

Poul Anderson, "Eutopia" (see here).

The History Of Westfall
Arabs, Vikings and Magyars destroyed Christendom;
civil wars destroyed the Islamic Empire;
European barbarians developed undisturbed;
eventually, crossing the Atlantic but lacking the power to exterminate the natives, they instead came to terms with them;
lacking industry, they adapted to the forests, plains, deserts and mountains;
despite remaining divided into petty states, like Norland and Dakoty, the Westfallers have developed radio, gas engines, electric motors, aircraft and nuclear weapons;
several realms have built a lunar base and sent expeditions to Ares;
whereas the American timeline is an example of man gone wrong, the Westfallers have something to teach the complacent Eutopians who sacrifice their humanity to rationality.

Like Anderson's "Losers' Night," this is a story with a double surprise ending. See here. At the end of "Eutopia," we might be so shocked by the revelation in the last word that we forget the earlier realization that "'...Westfall is also the Good Land.'" (p. 137)