Great Patriotic Wars, the long-delayed Third World War that begins and ends with massive nuclear exchanges. Much of Earth is devastated; civilization collapses and much of the surface is rendered temporarily uninhabitable.
-copied from here.
I have copied this passage from the Wikipedia article on the CoDominium because it confirms my earlier deduction that the Great Patriotic Wars are a delayed World War III.
The purpose of American future histories seems to be to move human beings out of the Solar System! - although interstellar travel was only just beginning at the very end of Robert Heinlein's original five volume Future History.
There is no doubt that dispersing humanity through space is a sure way to racial survival. Even ex-convicts living on Welfare or isolated colonies reduced to barbarism are at least living human populations which would not be possible on the surface of a single devastated planet. However, Poul Anderson in several works goes further, seeing an interstellar diaspora as the way to ensure that cultural diversity which is the essence of humanity.