One interesting note re: Native population decline in the Western Hemisphere. There are some estimates that upwards of 90% of the pre-Columbian native population died as a result of a smallpox pandemic. The smallpox was brought over by the Spanish conquistadors, but was likely an accidental infestation. This all occured by the time the so-called Pilgrims landed in Massachussetts in 1620.
The Western US, from the eastern edge of the Rocky Mountains (known locally as the Front Range) to the Mississippi River, and from the Dakotas to Texas, sits on an underground aquifer known as the Ogallala (ironically this is a Lakota Sioux name). The Ogallala is being depleted at an alarming rate by agriculture and ranching, which in turn has created a situation in which agricultural lands in the Western Great Plains are becoming unproductive. Large areas of Kansas, Nebraska and the Western Dakotas are losing population since farming is no longer viable.
Wait, there's more: the Lakota Sioux as a tribe have never recognized the government payoffs for their land. They signed treaties, broken by the US gov't., granting them the Black Hills (Paha Sapa), and most of Nebraska and the Dakotas, for "as long as the sun shines and the grass grows."
An excellent book for hearing the perspective of the Native Americans is "Neither Wolf Nor Dog: On Forgotten Roads with an Indian Elder" by Kent Nerburn. (ISBN I-57731-233-3) It was dictated by a Lakota elder and is a deeply moving account of how the Lakota see White culture.