system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How native americans lost so much of their territory so quickly to colonists

Was it really just diseases that decimated their numbers or were they just too trusting of the colonist until it was too late and their numbers and technology was just too great to fight back?
gpt
Lots of things.  

(1) The diseases had killed off vast numbers of people even in places that no Europeans visited.  By the time anyone set up colonies in North America, you were already looking at the post-apocalyptic leftovers of their civilization.  

(2) It really wasn't that fast.  You are looking at a stretch of basically 500 years.   That's a long damn time by anyone's reckoning.

(3) Numbers and technology did play a role.  The Natives only had their own groups to replace their numbers, but the colonists had a practically limitless supply of people and resources coming over from the Old World.

(4) There was no such thing as "The Native Americans."  There were many hundreds of nations, bands, and tribes that encountered the Europeans at different times and places.  Many native groups were also at war with each other.  There was never a point at which all natives took direction from a single leader or followed a single policy.  Trying to look at millions of diverse people as if they were a single Borg-like entity is a huge mistake.