There were a number of beliefs and values that were involved in the westward expansion of the United States. Let us look at three of the most important.
First, there was the idea of Manifest Destiny. This was the idea that God had destined the United States to spread itself across the continent.
Second, and closely related to the first, was the idea of white American supremacy. Americans believed that white people were superior to non-whites and that they therefore had the right to do things like taking land away from the Indians.
Finally, there was the idea of individualism and self-sufficiency. Many Americans felt that it was important to be able to live in a way that allowed them to rely on themselves. They felt that this made them more free than if they were to depend on others. This also influenced them to move west in hopes of being able to carve out a life in which they could have control of their own fate.