Why were Americans Indians treated so badly?

Ever since European settlers and traders landed in the Americas, their interactions with Natives have been checkered with both good and bad. The general explanation for the bad side of the interactions is twofold: First, the desire for economic success drove the English (and, later, Americans) to take advantage of Native Americans. Second, a cultural conception that European (then, American) culture is superior to Native cultures led to prejudice and other negatives, including the American government's systematic compulsion of Natives to settle in reservations.