Right on, Bob. The extraordinary affluence of North America was built by exploting a vast area of incredibly rich geography most of which had barely been affected at all yet by the millions of Native people who were living here before the Europeans came. Even the wildlife had not been seriously affected (other than the possible extinction of North American elephants in prehistoric times, presumably due to predation by bands of humans).
As you say, the frontier is gone now (except for the rapidly vanishing Amazon rainforest). The free stuff given by Nature is almost all gone. Yet the game goes on, as if nothing had changed. The people playing it now don't seem to know how to get off the hamster wheel that their recent ancestors set into motion...and what's that wheel really about? It's about making money.