( - 1801).
The Western United States, commonly referred to as the American West or simply "the West", traditionally refers to the region comprising the westernmost states of the United States. Because the U.S. expanded westward after its founding, the meaning of the West has evolved over time. Prior to about 1800, the crest of the Appalachian Mountains was seen as the western frontier. Since then, the frontier moved further west and the Mississippi River was referenced as the easternmost possible boundary of The West.
In the 21st century, the states including the Rocky Mountains to the West Coast are generally considered to comprise the American West.
The "West" had played an important part in American history; the Old West is embedded in America's folklore.