Here is the part of the description that could be misleading:
"with a population that probably never exceeded 20,000, lacking a written language and possessing no manufacturing base at all,"
Population:
The population figures expressed for the Iroquois are most likely under valued.
There are various political reasons for it, suffice to say when Louis and Clark reached the west coast of America, they said that there was as many Native Americans there as there was white people on the east coast.
Whenever a forester speaks in favor of clear cutting forests, they always claim how there was so many natives in the old days that there never was the primordial old growth forests.
I am inclined to believe there were at least 200,000 to 2 million Iroquois.
Perhaps the population was whittled down by unauthorized border incursions and disease.
Writing:
Also I disagree concerning the written language, according to a document I looked at, the Iroquois appeared to sign there name in their own language:
http://en.wikipedia.org/wiki/File:Ratification_of_Toronto_Purchase,_1805.jpg
If Pictographic/phonetic script is not considered writing, it can be claimed that the Japanese, Chinese, Egyptians and others have/had no writing.
Also there were was an English letter system available for them to use, if needed, so Europeans could read their names.
Manufacturing:
There is evidence of the production of smelted metals by Native Americans. Cabeza de Vaca spent 8 years among the natives and mentions it to the king, in his report.
The harmful environmental effects of the smelting process most likely kept the natives from mass producing on a large scale, because of different cultural values.
There is evidence in some places of ore extraction. However rather than making weapons, they used the ore for brightly colored paint and chemistry(British redcoats were made with an originally Aztec product).
Also there were wheels and plumbing confirmed in the south:
http://www.precolumbianwheels.com/
http://www.livescience.com/history/...cecom+(LiveScience.com+Science+Headline+Feed)