The Amazon was, allegedly, basically a garden at one point -- the natives the Spanish eventually encountered were just broken remains of a much larger civilization which had been successful and then disappeared.
http://www.amazon.com/1491-Revelations-Americas-Before-Colum...
I had the privilege to discuss the issue with the late Russell Means ( http://en.wikipedia.org/wiki/Russell_Means ) a few years ago.
What's disgusting is that the abuse continues to this very day.
First they were decimated, then they were forced into "reformation camps" to break their spirit, and then casino licenses and the like were thrown to them as a bone (and to corrupt and silence the more tempted or gullible with the easy money).
The government and various interested parties even try to take some of their supposedly "sovereign" reservation lands from them and/or poison them to get profitable minerals such as Uranium.
I met one of the creators of the movie in Chicago. One of the guys behind it, Jeff Spitz, is a very articulate advocate and has been following this story since 2000. His group followed up the movie with webisodes to update the story and use the movie to put pressure on the EPA.
Even at the time of the American Revolution, you see treaties with the Delaware Indians that are incredibly deferential, asking for their permission to cross Indian territory to fight the British.
The exterimination proceeded slowly over almost 100 years. We would make treaties, at first deferential then increasingly aggressive, to placate the Indians while slowly moving them off desirable land. American numbers grew while Indian numbers dwindled, until we got to the state that exists now, with them isolated to tiny little pockets of land.