alt Hacker NewsThat last sentence is doing all the work though. North American indians lived on the largest continuous region of agricultural land in the world, connected with perhaps the best river network, and never had above subsistence levels of wealth per capita.
It's hard to farm all that land when there are no horses to pull a plow, or pigs, cows, or sheep to raise for meat and milk and wool and manure. They didn't have all the crops that colonists crossed over with either: wheat, rice, and soybeans. The only crop of comparable productivity was corn, which was domesticated in South and Central America and had to be adapted to North America over many generations.
After they crossed the Bering Strait they also didn't receive any of the subsequent Old World advances in metallurgy, agriculture, chemistry, societal organization and so forth.
It's asking quite a lot of a relatively small population base to invent all those things independently while also lacking everything necessary to have comparable agricultural yields.
There was no Silk Road bringing gunpowder and paper and the Black Death to these societies. That means the native populations colonists encountered were the survivors of utterly cataclysmic epidemics. It's like if aliens brought a virus to Earth that killed 95% of the population and then they went "Hmm...these earthlings, they're not terribly productive are they?"
I'm not an anthropologist or an economist or a historian so there are many other factors I missed.