Same posts have talked of civilizations and complex societies before 'we' came and everyone got sick.
Other than the Anasazi (SP?) and the known centers in more latin America....how did this vast population manage without leaving large numbers of cities, engineering, or records other than burial mounds and oral history?
It simply does not appear to me, not greatly immersed in it, that civilization of any sort extended beyond a few - most gone before the white man came - centers. That does not indicate (to me) a huge population.
Mexico and Yucatan are filled to the brim with stone cities.
The Ohio Valley and the central part of the Mississippi Valley have immense pyramids built of earth.
South America now appears to have some of the oldest cities on Earth ~ older than those in Egypt or Mesopotamia in fact.
BTW, ancient Old World civilizations have only come to light in recent years. The Sumerians, for instance, who invented civilization, were unknown 200 years ago outside of the Bible, and then we didn't really recognize them (See the parts about Noah for example).
They are just now figuring out how many millions of people the Midwest and the Mid-Atlantic could support in late neolithic conditions, but it's in the millions.
Remember, when the Europeans began exploring the interior of what is now the United States in the mid 1500s (See: DeSoto) it was not heavily forested. The Indians kept the trees burned out to foster deer, other game, and agriculture. After they died from Old World diseases (circa 1648+) the forests returned in 50 years, and had yet another 120 years to grow!
Although the earliest pioneers thougth they were dealing primaeval forest, it was just overgrown farmland and pasture for nearly domesticated deer and wild buffalo.