Throughout history, Europeans had time and time again proved that one of their only priorities was to conquer land. From the time Christopher Columbus found North America, Europeans' idea of land expansion had exploded. They ruthlessly, throughout history, have taken land through force in order to obtain natural resources and exploit them in the name of convenience.
One of the largest examples of colonization happened in the mid-1800s. By this time, the United States government had been established and in retrospect, was fairly new; society had become more civilized, yet land and human populations were still under attack.
In this time period, people were still hungry for land and came up with many justifications to keep on taking it from natives. A prime example of this idea continued when President James Monroe declared the idea of Manifest Destiny, where he stated that it was God's will for the United States to continue to conquer land in western North America.