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 and the great rivers, such as the St. Lawrence, Connecticut, Hudson, Delaware, Susquehanna River and James.
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 and Mississippi River watershed, as far as the Rocky Mountains, they did not usually settle down. Actual French settlement in these areas was limited to a few very small villages on the lower Mississippi and in the Illinois Country. Likewise, the Dutch set up fur trading posts in the Hudson river valley, followed by large grants of land to 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 extension of European property rights to the new continent. The typical English settlements were quite compact and small--under a square mile. Conflict with the Native Americans arose out of political issues, i.e. 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 French colonial territory west of the Appalachians to the Mississippi River. Americans began moving across the Appalachians into areas such the Ohio Country and the New River Valley.
In the United States, the frontier was the term applied by scholars to the impact of the zone of transition where explorers, pioneers and settlers were arriving. That is, as pioneers moved into the frontier zone they were changed significantly by the encounter, and that change made them more American than the people back east. That is what Frederick Jackson Turner called "the significance of the frontier." For example, 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". On the Pacific Coast, settlement moved eastward. In New England, it moved north.
'Frontier' was borrowed into English from French in the 15th century with the meaning "borderland," the region of a country that fronts on another country (see also marches). The use of frontier to mean "a region at the edge of a settled area" is a special North American development. (Compare the Australian "outback".) In the Turnerian sense, "frontier" was a technical term that was explicated by hundreds of scholars.
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 Kentucky and Tennessee 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 Purchase, Oregon Country, and Mexican Cession, attracted hundreds of thousands of settlers. The question of whether the Kansas frontier would become "slave" or "free" was a spark of 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
When the Republican party came to power in 1860 they 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 was under 2 persons per square mile).
The American frontier was generally the most Western edge of settlement and typically more free-spirited in nature than 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.
A Canadian frontier thesis was developed by Canadian historians Harold Adams Innis and J. M. S. Careless. They emphasized the relationship between the center and periphery. Katerberg argues that "in Canada the imagined West must be understood in relation to the mythic power of the North." [Katerberg 2003] In Innis's 1930 work The Fur Trade in Canada, he expounded on what became known as the Laurentian thesis: that the most creative and major developments in Canadian history occurred in the metropolitan centers of central Canada and that the civilization of North America is the civilization of Europe. Innis considered place as critical in the development of the Canadian West and wrote of the importance of metropolitan areas, settlements, and indigenous people in the creation of markets. Turner and Innis continue to exert influence over the historiography of the American and Canadian Wests. The Quebec frontier showed little of the individualism or democracy that Turner ascribed to the American zone to the south. The Nova Scotia and Ontario frontiers were rather more democratic than the rest of Canada, but whether that was caused by the need to be self-reliant on the frontier itself or the presence of large numbers of American immigrants is debated.
The Canadian political thinker Charles Blattberg has argued that such events ought to be seen as part of a process in which Canadians advanced a "border"-- as distinct from a "frontier"--from east to west. According to Blattberg, a border assumes a significantly sharper contrast between the civilized and the uncivilized since, unlike with a frontier process, the civilizing force is not supposed to be shaped by that which it is civilizing. Blattberg criticizes both the frontier and border "civilizing" processes.
The pattern of settlement of the Canadian prairies began in 1896, when the American prairie states had already achieved statehood. Pioneers then headed north to the "Last Best West." Before settlers began to arrive, the North West Mounted Police was dispatched to the region. When settlers began to arrive, a system of law and order was already in place and the Dakota lawlessness for which the American "Wild West" was famed did not occur in Canada. Before settlers arrived, the federal government also sent teams of negotiators to meet with the Native peoples of the region. In a series of treaties, the basis for peaceful relations was established and the long wars with the Natives that occurred in the United States largely did not spread to Canada. Like their American counterparts, the Prairie provinces supported populist and democratic movements in the early 20th century. 
In the European Union, the frontier is a term used to describe the region beyond the expanding borders of the European Union. The European Union has designated the countries surrounding it as part of the European Neighbourhood. This is a region of primarily less-developed countries, many of which aspire to become part of the European Union itself. Current applicants include Turkey and many small countries in the Balkans and South Caucasus. Romania and Bulgaria joined the European Union in 2007. Proposals to admit Turkey have been debated but are now currently stalled, partly on the ground that Turkey is beyond Europe's historic frontier and it is yet to comply with the 35 point policy areas set out by the EU. If all or most East European states become members, the frontier may be the boundaries with Russia and Turkey.