Following the victory of the United States in the American Revolutionary War and the signing Treaty of Paris in 1783, the United States gained formal, if not actual, control of the British lands west of the Appalachians. Many thousands of settlers, typified by Daniel Boone, had already reached KentuckyTennessee, and adjacent areas. Some areas, such as the Virginia Military District and the Connecticut Western Reserve (both in Ohio), were used by the states as rewards to veterans of the war. How to formally include these new frontier areas into the nation was an important issue in the Continental Congress of the 1780s and was partly resolved by the Northwest Ordinance (1787). The Southwest Territory saw a similar pattern of settlement pressure.

For the next century, the expansion of the nation into these areas, as well as the subsequently acquired Louisiana PurchaseOregon Country, and Mexican Cession, attracted hundreds of thousands of settlers. Whether the Kansas frontier would become “slave” or “free” kindled the American Civil War. In general before 1860, Northern Democrats promoted easy land ownership and Whigs and Southern Democrats resisted. The Southerners resisted Homestead Acts because it supported the growth of a free farmer population that might oppose slavery.

When the Republican Party came to power in 1860 it promoted a free land policy — notably the Homestead Act of 1862, coupled with railroad land grants that opened cheap (but not free) lands for settlers. In 1890, the frontier line had broken up (Census maps defined the frontier line as a line beyond which the population density was under 2 inhabitants per square mile or 0.8 inhabitants per square kilometre).

The effect of the frontier upon popular culture was enormous, in dime novels, Wild West shows, and, after 1910, Western movies set on the frontier.

The American frontier was generally the westernmost edge of a settlement and typically more free-spirited than in the East because of its lack of social and political institutions. The idea that the frontier provided the core defining quality of the United States was elaborated by the historian Frederick Jackson Turner, who built his Frontier Thesis in 1893 around this notion. Subsequently, the frontier has also been described as the point of contact between two cultures, where contact led to exchanges that affected both cultures.

In popular culture, Alaska: The Last Frontier is an American reality cable television series about Alaskan pioneers, Yule and Ruth Kilcher, at their homestead 11 miles outside of Homer.