I believe they used the phrase "Manifest Destiny." In other words, they believed that it was their destiny to have the land and to build upon it.
The damage outweighed the benefits to the American people because it meant they got to "have more." In other words, more money.
The government could have made an agreement with the natives and possibly allowed them to continue living on the land, perhaps, that would have caused less wars or battles in the end.
I think the control of Boston early in the Revolutionary War was important because if it never occurred, we would not have states and would all be independent
Most of the scholars preached against the Mongol rule so the Mongols in power made sure that the scholars do not get high positions in the new government.