In American history the frontier is the process of settlement of new lands in the West, and the impact on the frontiersmen and the nation at large. As pioneers moved west they changed their customs, behavior and values and became more "American"; Frederick Jackson Turner called this "the significance of the frontier," Turner argued in 1893, one change was that unlimited free land in the zone was available and thus offered the psychological sense of unlimited opportunity, which in turn had many consequences, such as optimism, future orientation, shedding of restraints due to land scarcity, and wastefulness of natural resources.
Throughout American history, the expansion of settlement was largely from the east to the west, and thus the frontier is often identified with "the west." In New England, it moved north, so that Maine and Vermont had frontier characteristics.
See also: Colonial America
In the earliest days of European settlement of the Atlantic coast, the frontier was essentially any part of the forested interior of the continent beyond the fringe of existing settlements along the coast.
English, French, Spanish and Dutch patterns of expansion and settlement were quite different. Only a few thousand French migrated to Canada; these habitants settled in villages along the St. Lawrence river, building communities that remained stable for long stretches; they did not leapfrog west the way the Americans did. Although French fur traders ranged widely through the Great Lakes region they seldom settle down. Likewise, the Dutch set up fur trading posts in the Hudson River valley, followed by large grants of land to rich landowning patroons who brought in tenant farmers who created compact, permanent villages. They did not push westward. 
In contrast, the English colonies generally pursued a more systematic policy of widespread settlement of the New World for cultivation and exploitation of the land, a practice that required the application of legal property rights to the new conditions. The typical English settlements were quite compact and small--under a square mile. Conflict with the Native Americans arose out of political issues, viz. who would rule. Early frontier areas east of the Appalachian Mountains included the Connecticut River valley. The French and Indian Wars of the 1760s resulted in a complete victory for the British, who took over the lands west to the Mississippi River. By the early 1770s Americans were moving across the Appalachians into western Pennsylvania, Kentucky, Tennessee and Ohio.
Early National Era, 1770s-1830s
After the Revolutionary war ended (1781), the Americans in large numbers poured into the west. In some areas they had to battle the Indian tribes. No Indians lived in Kentucky but they sent raiding parties to stop the newcomers, like Abe Lincoln's grandfather (who was scalped in 1786 near Louisville.) The War of 1812 marked the final confrontation between major Indian forces trying to stop the advance, with British aid. American frontier militiamen under Andrew Jackson defeated the Creeks and opened the Southwest, while militia under William Henry Harrison defeated the Indian-British alliance at a battle in Canada. The death in battle of the Indian leader Tecumseh dissolved the coalition of hostile Indian tribes. In general the frontiersmen battled the Indians with little help from the U.S. Army or the federal government. Indeed, the regular army set up a line of forts designed to keep the Indians and settlers apart.
As settlers poured in the new areas went through the territorial stage and became states, typically dropping the legalistic practices favored by eastern upper classes, and adopting more democracy and more egalitarianism.
Later frontier, 1830s-1890
Debate on Turner's interpretation
Kearns (1998) examines the environmentalism of William Cronon and Donald Worster, and the revisionist moralism of Richard White and Patricia Limerick, who reject Turner as too favorable toward white men.
Since the 1970s the "new western historians" have attacked Turner's model. They have condemned the frontier thesis for its Euro-centric and racist assumptions, ridiculing Turner for his depiction of enlightened whites and savage natives and for discounting Indian agency. They assailed Turner's argument that the frontier created America character and ideology by revealing how Americans drew upon European antecedents and their own experiences in urban settings. Other maintain that the frontier was neither especially democratic nor equal. Nevertheless the Turnerians have counterattacked, saying that the critics confuse 21st century moralistic sensibilities with historical reality. Turner's model, they note, was not about the Indians (who Turner wrote about elsewhere), but rather about the impact of the frontier on the frontiersmen and all Americans. Agreeing that the frontiersmen did not jettison all European ideas, the Turnerians argue they decisively remoulded and reshaped them to meet American conditions. The critics who suggest that democracy emerged from boss-ridden urban machines like Tammany Hall have surely misunderstood what American democracy means.
- French settlement in these areas was limited to a few very small villages such as Kaskaskia. Clarence Walworth Alvord, The Illinois Country 1673-1818 (1918)
- Arthur G. Adams, The Hudson Through the Years (1996); Sung Bok Kim, Landlord and Tenant in Colonial New York: Manorial Society, 1664-1775 (1987)
- Allan Kulikoff, From British Peasants to Colonial American Farmers (2000)