The history within my world doesn't really seem to reflect the same history in others. The land you call America exists in my world, but it isn't called that.
[Mm... she hums in thought.]
Mankind has flourished and then nearly wiped out more than once in the last ten thousand years-- whether because of famine or war. It might have been a kingdom or nation from within the past? I'm aware of England after all. Or maybe it's named America in the future?