The American frontier comprises the
folklore, and cultural expression of life in the forward wave of American expansion that began with English colonial settlements in the early 17th century and ended with the admission of the last mainland territories as states in 1912. "Frontier" refers to a contrasting region at the edge of a European-American line of settlement. American historians cover multiple frontiers but the folklore is focused primarily on the conquest and settlement of Indian lands, west of the
Mississippi River, in what is now the Midwest, Texas, the Great Plains, the Rocky Mountains, the Southwest, and the West Coast.
This era of massive migration and settlement was particularly encouraged by the Colonial and early United States government following the
Louisiana Purchase, and coined the term and political philosophy known as "
Enormous popular attention in the 19th and early 20th century media focused on the
Western United States in the second half of the 19th century, a period sometimes called the Old West, or the Wild West, the theme of which typically exaggerated the romance, anarchy, and chaotic violence of the period for greater dramatic effect. This eventually inspired the
Western genre of film, which spilled over into
comic books, and children's toys, games and costumes.
As defined by Hine and Faragher, "frontier history tells the story of the creation and defense of communities, the use of the land, the development of markets, and the formation of states." They explain, "It is a tale of conquest, but also one of survival, persistence, and the merging of peoples and cultures that gave birth and continuing life to America."
 Through treaties with foreign nations and
native tribes; political compromise; military conquest; establishment of law and order; the building of farms, ranches, and towns; the marking of trails and digging of mines; and the pulling in of great migrations of foreigners, the United States expanded from coast to coast, fulfilling the dreams of
Manifest Destiny. Historian
Frederick Jackson Turner in his "
Frontier Thesis" (1893) theorized that the frontier was a process that transformed Europeans into a new people, the Americans, whose values focused on equality,
optimism, as well as
individualism, self-reliance, and even
violence. Thus, Turner's Frontier Thesis proclaimed the westward frontier to be the defining process of American history.
As the American frontier passed into history, the myths of the West in fiction and film took firm hold in the imagination of Americans and foreigners alike. In David Murdoch's view,
America is exceptional in choosing its iconic self-image: "No other nation has taken a time and place from its past and produced a construct of the imagination equal to America's creation of the West."
United States territories in 1789
United States territories in 1845–46
United States territories in 1884–89
United States territories in 1912