Well, it sort of was. It’s just that the waves of illness brought on by contact with the Old World decimated the indigenous population. By the time that significant surveys of the interior of North America (I’m excluding Mexico here) were conducted in the 16th and 17th centuries, the bulk of the populace had perished, leaving behind vast tracts of land populated by only a handful of survivors. The large nation-state civilizations like the Mound-builders had ceased to exist.
Even at their densest, are you saying Indians had mapped out the continent and divvied it up?