Americans in the nineteenth century believed they were entitled to the lands west of the Mississippi for a number of reasons, most of which were encompassed by the ideology that came to be known as "manifest destiny." Some of the key components of this ideology were as follows:
- the United States was a progressive nation, the only truly democratic nation on earth. As such, the spread of America meant the spread of democratic ideals throughout the continent.
- the people who inhabited the Trans-Mississippi West, it was believed, had not "improved" the lands they lived on and therefore had no right to them. Americans, they argued, would farm, mine, and otherwise put the vast resources of the West to good use.
- expansion into the West would continue to promote economic equality, which was the foundation of political equality.
- God had chosen the American people to bring Christianity (as well as democracy) to the indigenous peoples of the West.
- American culture was understood to be superior to that of Native Americans as well as Mexican peoples that controlled parts of the West.
All of these ideals, some of which were contradictory, some mutually reinforcing, convinced Americans that they had the God-given right to move westward.