Westward expansion played a major role in American history. American expansion brought the nation wealth through minerals, farmland, and new ports. It also gave an ever-expanding population room to grow. Westward expansion allowed people to look for new beginnings when faced with economic or personal ruin in the East.

Westward expansion has not been entirely positive in American history. Each time the nation expanded, Native Americans lost land due to extermination and treaties that unfairly favored pioneers and miners. The environment in the West suffered notably, as well, with the destruction of the American prairie and several animal species. Land speculation helped to fuel some of the economic downturns in the early Republic. Finally, American imperialism caused the United States to go to war, most notably with Mexico in 1846. The Mexican Cession forced the issue of slavery to the forefront of the national consciousness and may have helped to fuel the anger that led to the Civil War in 1861.

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.