A frontier is a political and geographical term referring to areas near or beyond a boundary, particularly zones at the edge of settled or governed territory. The concept carries distinct meanings in different national and cultural contexts, but broadly describes a transitional zone between an established civilization and unknown, ungoverned, or contested land. In colonial and post-colonial history, frontiers played a central role in the expansion of European powers into the Americas, Asia, and Australia. Countries such as Brazil, Argentina, Chile, and the United States each developed distinct frontier cultures, mythologies, and policies shaped by encounters with indigenous peoples, geographic conditions, and imperialist ambitions. In the United States, the concept was most influentially theorized by historian Frederick Jackson Turner, whose Frontier Thesis (1893) argued that the frontier experience was the defining force in shaping American democracy and national character. Canada developed a parallel historiographical tradition through scholars such as Harold Adams Innis. Beyond the Americas, frontier zones shaped imperial expansion in Russia, China, and the Indian subcontinent. The word "frontier" entered English from French in the 15th century with the meaning "borderland"; its use to describe the edge of settled territory is a distinctly North American development.
Australia
The term "frontier" was frequently used in colonial Australia in the meaning of country that borders the unknown or uncivilised, the boundary, border country, the borders of civilisation, or as the land that forms the furthest extent of what was frequently termed "the inside" or "settled" districts.See e.g. Parliamentary Debate April 14 Legislative Assembly of NSW (Australian April 14, 1848, p.4 Robinson) The "outside" was another term frequently used in colonial Australia; this term covered not only the frontier but the districts beyond. Settlers at the frontier thus frequently referred to themselves as "the outsiders" or "outside residents" and to the area in which they lived as "the outside districts". At times one might hear the "frontier" described as "the outside borders".see e.g. Sydney Morning Herald June 6, 1851 p.2g; South Australian Register, Moreton Bay Courier Feb 16, 1861, p2 and 2 April 1861, p.3 re 'The Native Police'; see Queensland Parliamentary Debate (Attorney-General Pring) (Brisbane Courier, July 27, 1861, p5); Queensland Parliamentary Debate 20 August 1863; Brisbane Courier, Aug 22, 1863 (Editorial). However the term "frontier districts" was seemingly used predominantly in the early Australian colonial newspapers whenever dealing with skirmishes between black and white in northern New South Wales and Queensland, and in newspaper reports from South Africa, whereas it was seemingly not so commonly used when dealing with affairs in Victoria, South Australia, and southern New South Wales. The use of the word "frontier" was thus frequently connected to descriptions of frontier violence, as in a letter printed in the Sydney Morning Herald in December 1850 which described murder and carnage at the northern frontier and calling for the protection of the settlers saying: "...nothing but a strong body of Native Police will restore and keep order in the frontier districts, and as the squatters are taxed for the purpose of such protection".Sydney Morning Herald Dec 24, 1850, p.3s.
Brazil
Sertão
Early Portuguese colonization of South America concentrated near the sea, being described by friar Vicente do Salvador as "crabs hugging the coast". As a result, Brazilian colonists developed their own idea of the continental hinterland as the Sertão, a massive and mysterious frontier thought to be either void of human life or plagued by indigenous raids, while tantalizingly full of untapped resources. With the coast dominated by sugar plantations in the 17th century, colonists known as Sertanejos expanded cattle raising into the interior of the Northeast through a series of wars against the native peoples known as the Barbarian Wars. The conquered area, roughly equal to the entire Caatinga biome, became a hub for Brazilian cattle raising and cotton production. After the Brazilian Great Drought of 1877–1878, the area became known for government mismanagement and violent outlaws that created the modern frontier mythology of the Cangaço.
Bandeiras
São Vicente was the first Portuguese settlement in South America, eventually leading to the creation of São Paulo dos Campos de Piratininga as the main Portuguese village above the Serra do Mar. This location isolated the inhabitants from contact with Portugal proper by the sea, while placing them at an advantageous position to access the Brazilian Highlands. These Paulistas developed a frontier culture known as Caipira, and engaged in expeditions to the continent's interior known as entradas and bandeiras. The goal of the expeditions were to enslave indigenous peoples in the deep interior and to look for rare minerals. Those who partook in these expeditions came to be known as Bandeirantes, and they raided Jesuit missions and indigenous villages alike.
The expeditions reached well beyond the Treaty of Tordesillas limits agreed by Portugal, including the destruction of the Spanish Guayrá province. Due to their reputation, Bandeirantes like Domingos Jorge Velho were often employed by Portuguese colonial officials to destroy resistance groups in the frontier, such as the main free Afro-Brazilian community in the Quilombo dos Palmares and indigenous confederations in the Northeast. The discovery of gold in Minas Gerais in 1690 and resulting gold rush created friction between the Bandeirantes, who claimed full ownership of the mines, and the Portuguese government and other colonists. The War of the Emboabas expelled the Bandeirantes from Minas Gerais, who continued their expeditions westward finding new gold mines in modern Goiás, Mato Grosso and Rondônia, with the Guaporé River marking the westernmost limit of Bandeirante activity, now thousands of miles from the original Tordesillas line. Wanting to secure the new valuable and rich western frontier, Portugal negotiated with Spain the Treaty of Madrid in 1750 to formally annex all Bandeirante conquests into the State of Brazil, adding up to almost half of South America, as compensation for Spain's violation of Tordesillas in the Philippines. The treaty also exchanged Colônia do Sacramento for Misiones Orientales, but the native Guaraní resistance to the Bandeirante raids against the missions escalated into the Guaraní War, undoing the treaty. Nevertheless, following the Independence of Brazil in 1822 and border conflicts with its neighbors, all Bandeirante conquests were recognized as Brazilian territory.
Amazon
The first Portuguese expedition into the Amazon happened in 1613 under Francisco Caldeira Castelo Branco, who founded the city of Belém to control the mouth of the Amazon River. In 1637 Pedro Teixeira carried out an expedition from Belém to Quito and claimed most of the Amazon basin for the Portuguese crown. Most colonial activity in the region were Portuguese Jesuit missions to convert native groups and the extraction of tropical goods like Brazil nuts, cocoa beans and guarana. Portuguese colonists would intermarry with local indigenous women, creating a unique Amazonian people known as Ribeirinhos. The Portuguese government, concerned about the Amazon's settlements vulnerability and lack of large economic activity compared to its other holdings in South America, detached them from the State of Brazil and created a second colony, the State of Maranhão to directly administer them. During this period the Atlantic slave trade was directed into the ports of Belém and São Luís, resulting in a significant black population in the territory. In 1775 the colonies were rolled back into the State of Brazil.
By independence, the Amazon became a source of international prestige for Brazil, as well as the least explored frontier. The precise borders with its neighbors were still undefined, including with the European powers in the Guianas. The late 19th century Amazon rubber cycle saw for the first time the Amazon become an attractive area for mass settlement of Brazilians. Tens of thousands of internal migrants worked extracting rubber for rubber barons, and cities like Manaus soared economically, becoming symbols of the Brazilian Belle Époque. The prosperity brought the need to finally settle the borders of the region for good, resulting in frontier skirmishes such as the Acre War, the Amapá Question and the Pirara Dispute. The end of the rubber boom would begin a decline in the region, identified by military strategists and federal politicians as a security risk due to the frontier not being fully settled. The Rubber soldiers program during World War II, the establishment of the Free Economic Zone of Manaus and the Trans-Amazonian Highway are all attempts by the Federal Government of Brazil to occupy and protect its claim to the Amazon frontier.
March to the West
The March to the West was a political, economic and ideological programme idealized by President Getúlio Vargas during the 1930s. It perceived the sparsely populated frontiers of Brazil as a missed opportunity and security risk. Writer Cassiano Ricardo was the main ideologue of the project, combining the then popular influences of Brazilian Modernism and Brazilian nationalism into a romantic and deterministic narrative that placed the frontier as the great destiny of the Brazilian people. The ideological drive for Federal projects to populate the interior would be maintained throughout the Vargas era, the Fourth Brazilian Republic and even during the Military dictatorship. These projects included the establishments of the Federal territories of Brazil in the frontier, the Construction of Brasilia as the new capital, the building of the Itaipu Dam, creation of colonization companies like Sinop, and the Brazilian Agricultural Research Corporation to develop genetically modified crops that can grow in the Cerrado climate.
Hispanic America
Argentina The southern Indigenous frontier of the Viceroyalty of the Río de la Plata was the southern limit into which the Viceroyalty could exert its rule. Beyond this lay territories de facto controlled by Indigenous peoples who inhabited the Pampas and Patagonia. These group were mainly the Tehuelche, Pehuenche, Mapuche, and the Ranqueles.
Various military campaigns and peace treaties were arranged by the Spanish in order to either stop indigenous incursions in Spanish lands or to advance the frontier into indigenous territory. In the 1870s, to counter the cattle raids (and the native peoples on horseback), Argentina constructed a deep trench, called Zanja de Alsina, to prevent cattle from being driven west and establish a boundary to the raiding tribes in the Pampas.
Under General Julio Argentino Roca, the Conquest of the Desert extended Argentine power into Patagonia.
Bolivia