structural:scholar_edition, structural:expansion
End of the frontier

Following the 1890 U.S. census, the superintendent announced that there was no longer a clear line of advancing settlement, and hence no longer a contiguous frontier in the continental United States. When examining the later 1900 U.S. census population distribution results though, the contiguous frontier line does remain. But by the 1910 U.S. census, only pockets of the frontier remain without a clear westward line, allowing travel across the continent without ever crossing a frontier line.

Virgin farmland was increasingly hard to find after 1890—although the railroads advertised some in eastern Montana. Bicha shows that nearly 600,000 American farmers sought cheap land by moving to the Prairie frontier of the Canadian West from 1897 to 1914. However, about two-thirds of them grew disillusioned and returned to the U.S. Despite this, homesteaders claimed more land in the first two decades of the 20th century than the 19th century. The Homestead Acts and proliferation of railroads are often credited as being important factors in shrinking the frontier, by efficiently bringing in settlers and required infrastructure. The increased size of land grants from 160 to 320 acres in 1909 and then rangeland to 640 acres in 1916 accelerated this process. Barbed wire is also reasoned to reduce the traditional open range. In addition, the growing adoption of automobiles and their required network of adequate roads, first federally subsidized by the Federal Aid Highway Act of 1916, solidified the frontier's end.

The admission of Oklahoma as a state in 1907 upon the combination of the Oklahoma Territory and the last remaining Indian Territory, and the Arizona and New Mexico territories as states in 1912, marks the end of the frontier story for many scholars. Due to their low and uneven populations during this period though, frontier territory remained for the meantime. Of course, a few typical frontier episodes still happened such as the last stagecoach robbery occurred in Nevada's remaining frontier in December 1916. A period known as "The Western Civil War of Incorporation" that often was violent, lasted from the 1850s to 1919.

The Mexican Revolution also led to significant conflict reaching across the US-Mexico border which was still mostly within frontier territory, known as the Mexican Border War (1910–1919). Flashpoints included the Battle of Columbus (1916) and the Punitive Expedition (1916–1917). The Bandit War (1915–1919) involved attacks targeted against Texan settlers. Also, skirmishes involving Natives happened as late as the Bluff War (1914–1915) and the Posey War (1923).

The westward expansion of American influence and jurisdiction across the Pacific in the late 19th century was in some sense a new " Asia–Pacific frontier", with Frederick Jackson Turner arguing this to be a necessary element of the U.S.'s growth, as its identity as a civilized and ideals-based nation depended on constantly overcoming a savage 'other'.

Alaska was not admitted as a state until 1959. The ethos and storyline of the "American frontier" had passed.