[dennisw]

Very interesting and my guess is true

[hoosierham]

The indigenous peoples in America could have,maybe were, devasted by diseases brought by European explorers.

Just look at abandoned farms and homes in the eastern United States.There are buildings not far from me almost hidden by trees after less than twenty years of standing unused.Former hay-fields returning to forest in like time.

Only in desert climates do man-made structures stand evident for long times.In temperate or tropical zones vegetation quickly grows around and over everything.