Westward expansion affected American history in a number of ways. Among them are:
- It made America richer. The US expanded out into areas that are now the breadbasket of the country and into areas with immense mineral wealth. This helped make the country rich and therefore powerful.
- It made America tend towards the ideas of manifest destiny and imperialism. It helped Americans feel superior to others and it helped make them feel they deserved further expansion.
- It made America more democratic and individualistic. This is the Frederick Jackson Turner thesis. This says that expanding allowed Americans to live on the frontier where they learned to be more self-sufficient and egalitarian.
In these ways, westward expansion changed American history by profoundly changing the economic situation in the country and by changing the attitudes of the people in a number of ways.