In the years before the plague turned America into The Stand, a sailor named Giovanni da Verrazzano sailed up the East Coast and described it as "densely populated" and so "smoky with Indian bonfires" that you could smell them burning hundreds of miles out at sea. Using your history books to understand what America was like in the 100 years after Columbus landed there is like trying to understand what modern day Manhattan is like based on the post-apocalyptic scenes from I Am Legend.
"They call it 'The city that never sleeps' because the only guy who lives there is a notoriously sarcastic rapper."
Historians estimate that before the plague, America's population was anywhere between 20 and 100 million (Europe's at the time was 70 million). The plague would eventually sweep West, killing at least 90 percent of the native population. For comparison's sake, the Black Plague killed off between 30 and 60 percent of Europe's population.
While this all might seem like some heavy shit to lay on a bunch of second graders, your high school and college history books weren't exactly in a hurry to tell you the full story. Which is strange, because many historians believe it is the single most important event in American history. But it's just more fun to believe that your ancestors won the land by being the superior culture.
Yay for apocalypse profiteering!