I dunno. I think it just goes back to the Puritans and all those groups who think that the America is the real Promised Land and that they'll be privileged in all sorts of ways. The comments by LaHaye, Hal Lindsey, and others of their ilk seem to indicate that a large part of their beliefs are tied into some superpatriotic belief in America=God's Gift to the world.
There were people with this sort of attitude on the news advocating the Left Behind series not too long ago, and their comments came across with the geniune belief that God was raising America up to "rule the world" or some such nonsense. It's a scary idea, to think you and your country have been chosen by God. Scary indeed.
Beware the Groove