[rdl]

What happened, from what I've read, is that initial contact put enough European disease into the population that the population and society collapsed; it was thus much easier for Europeans settling here to win.

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...