[suburbanite]

It's important to remember to that by the time the first settlers arrived on the East Coast, native populations across North America had already been ravaged by smallpox, theorized to have been brought in during Ponce De Leon's expedition to Florida in 1513. Smallpox spread up the Mississippi through established trade routes all the way into the interior, completely wiping out the largest permanent settlements in North America created by the Mississippians. Mesoamerican populations would be similarly devastated, but the Spanish still had the experience of encountering the heart of a Native American civilization untouched by old world diseases. Extrapolating those pre-columbian populations based on the situation at first contact is a much cleaner exercise.

In contrast, by the time Europeans encountered the historically most densely populated areas in the U.S., they were nothing more than dirt mounds and forests no longer tamed by Native American forest fire practices. The people that did survive were nomadic in nature and less likely to encounter the spread of smallpox, leading to the inaccurate perception that North America had always been a place of empty untouched wilderness and small, unsophisticated roaming tribes. The remnants of North American civilizations were not encountered until hundreds of years after their downfall. This combined with the fact that they rarely used stone construction or kept permanent records makes estimating their pre-columbian populations a very difficult task.

There is no doubt that the vast majority of the hemisphere's population sat between the Rio Grande and Andes Mountains, but at the same time, North America was not a completely empty wilderness during pre-columbian times.