What part of the country is considered where the west expands?

The area commonly associated with the westward expansion of the United States is the western region, particularly the Great Plains and the Rocky Mountains. This expansion primarily occurred in the 19th century as settlers moved into territories acquired through treaties, purchases, and conflicts. States like California, Oregon, and Texas played significant roles during this period, symbolizing the pursuit of new opportunities and the idea of Manifest Destiny. The westward expansion significantly shaped the cultural and economic landscape of the nation.