Borders are generally defined as geographical boundaries, imposed either by features such as oceans and terrain, or by political entities such as governments, sovereign states, federated states, and other subnational entities. Political borders can be established through warfare, colonization, or mutual agreements between the political entities that reside in those areas.
Some borders—such as most states' internal administrative borders, or inter-state borders within the Schengen Area—are open and completely unguarded. Most external political borders are partially or fully controlled, and may be crossed legally only at designated border checkpoints; adjacent border zones may also be controlled. For the purposes of border control, airports and seaports are also classed as borders. Most countries have some form of border control to regulate or limit the movement of people, animals, and goods into and out of the country. Under international law, each country is generally permitted to legislate the conditions that have to be met in order to cross its borders, and to prevent people from crossing its borders in violation of those laws.
Buffer zones may be set up on borders between belligerent entities to lower the risk of escalation. While border refers to the boundary itself, the area around the border is called the frontier.
History
In the pre-modern world, the term border was vague and could refer to either side of the boundary, thus it was necessary to specify part of it with borderline or borderland. During the medieval period the government's control frequently diminished the further people got from the capital. Therefore borderland (especially impassable terrain) attracted many outlaws, as they often found sympathizers.
In the past, many borders were not clearly defined lines; instead there were often intervening areas often claimed and fought over by both sides, sometimes called marchlands. Special cases in modern times were the Saudi Arabian–Iraqi neutral zone from 1922 to 1991 and the Saudi Arabian–Kuwaiti neutral zone from 1922 until 1970. In modern times, marchlands have been replaced by clearly defined and demarcated borders.
Classification
Political borders
Political borders are imposed on the world through human agency. That means that although a political border may follow a river or mountain range, such a feature does not automatically define the political border, even though it may be a major physical barrier to crossing.
Political borders are often classified by whether or not they follow conspicuous physical features on the earth. William Miles said that Britain and France traced close to 40% of the entire length of the world's international boundaries.
Natural borders
Natural borders are geographical features that present natural obstacles to communication and transport. Existing political borders are often a formalization of such historical, natural obstacles.
Some geographical features that often constitute natural borders are:
Oceans: oceans create very costly natural borders. Very few countries span more than one continent. Only very large and resource-rich states are able to sustain the costs of governance across oceans for longer periods of time.
Rivers: Some political borders have been formalized along natural borders formed by rivers. If a precise line is desired, it is often drawn along the thalweg, the deepest line along the river.
Lakes: larger lakes create natural borders.
Forests: denser jungles or forests can create strong natural borders.
Mountain ranges: Many nations have their political borders defined along mountain ranges, often along a drainage divide.
Throughout history, technological advances have reduced the costs of transport and communication across the natural borders. That has reduced the significance of natural borders over time. As a result, political borders that have been formalized more recently, such as those in Africa or Americas, typically conform less to natural borders than very old borders, such as those in Europe or Asia, do.
Landscape borders
A landscape border is a mixture of political and natural borders. One example is the defensive forest created by China's Song dynasty in the eleventh century. Such a border is political in the sense that it is human-demarcated, usually through a treaty. However, a landscape border is not demarcated by fences and walls but instead landscape features such as forests and water bodies. It is different from a natural border, however, in the sense that the border landscape is not natural but human-engineered. Such a landscape usually differs from the borderland's natural geography and its building requires tremendous human labour and financial investment.
Geometric borders
Geometric boundaries are formed by straight lines (such as lines of longitude), or occasionally arcs (such as lines of latitude or the Pennsylvania/Delaware border), regardless of the physical and cultural features of the area. Such political boundaries are often found around the states that developed out of colonial holdings, such as in North America, Africa and the Middle East. The Canada–United States border follows the 49th parallel for roughly 2,175 miles (3,500 km) from Lake of the Woods (Ontario and Minnesota) west to the Pacific Ocean.
Fiat borders
A generalization of the idea of geometric borders is the idea of fiat boundaries by which is meant any sort of boundary that does not track an underlying bona fide physical discontinuity (fiat, Latin for "let it be done", a decision). Fiat boundaries are typically the product of human demarcation, such as in demarcating electoral districts or postal districts.
Relic borders
A relic border is a former boundary, which may no longer be a legal boundary at all. However, the former presence of the boundary can still be seen in the landscape. For instance, the boundary between East and West Germany is no longer an international boundary, but it can still be seen because of historical markers on the landscape; it remains a cultural and economic demarcation in Germany. Other examples include the Demilitarized Zone between North and South Vietnam (defunct since 1975) and the border between North and South Yemen (defunct since 1990). Occasionally a relic border is reconstituted in some form, for example the border between British Somaliland and Italian Somaliland ceased to exist when the two colonies merged to form the independent state of Somalia in 1960, however when the former British Somaliland declared independence in 1991 it claimed the former British-Italian line as its eastern border.
Lines of control
A line of control (LoC) refers to a militarized buffer border between two or more nations that has yet to achieve permanent border status. LoC borders are typically under military control and are not recognized as an official international border. Formally known as a cease-fire line, an LoC was first created with the Simla Agreement between India and Pakistan. Similar to a cease-fire line, an LoC is typically the result of war, military stalemates and unresolved land ownership conflict.
Maritime borders
A maritime border is a division enclosing an area in the ocean where a nation has exclusive rights over the mineral and biological resources, encompassing maritime features, limits and zones. Maritime borders represent the jurisdictional borders of a maritime nation and are recognized by the United Nations Convention on the Law of the Sea.
Maritime borders exist in the context of territorial waters, contiguous zones, and exclusive economic zones; however, the terminology does not encompass lake or river boundaries, which are considered within the context of land boundaries.
Some maritime borders have remained indeterminate despite efforts to clarify them. This is explained by an array of factors, some of which illustrate regional problems.
Airspace borders
Airspace is the atmosphere located within a country's controlled international and maritime borders. All sovereign countries hold the right to regulate and protect air space under the international law of Air sovereignty. The horizontal boundaries of airspace are similar to the policies of "high seas" in maritime law. Airspace extends 12 nautical miles from the coast of a country and it holds responsibility for protecting its own airspace unless under NATO peacetime protection. With international agreement a country can assume the responsibility of protecting or controlling the atmosphere over International Airspaces such as the Pacific Ocean. The vertical boundaries of airspace are not officially set or regulated internationally. However, there is a general agreement of vertical airspace ending at the point of the Kármán line. The Kármán line is a peak point at the altitude of 62 mi (100 km) above the Earth's surface, setting a boundary between the atmosphere (airspace) and outer space (which is governed by space law).
Frontier
The frontier is a border that is open-ended to one side, identifying an expanding borderland to one side.
This type of border can be fairly abstract and has been identified as a particular state of mind for human activity. As such frontiers have been applied to borderlands identifying and claiming them as terra nullius, such as Marie Byrd Land in West Antarctica, the only territory in Antarctica unclaimed by any sovereign nation.
Types of border regulation
In places where smuggling, migration, and infiltration are a problem, many countries fortify borders with fences and barriers, and institute formal border control procedures. These can extend inland, as in the United States where the U.S. Customs and Border Protection service has jurisdiction to operate up to 100 miles from any land or sea boundary. On the other hand, some borders are merely signposted. This is common in countries within the European Schengen Area and on rural sections of the Canada–United States border. Borders may even be completely unmarked, typically in remote or forested regions; such borders are often described as "porous". Migration within territorial borders, and outside of them, represented an old and established pattern of movement in African countries, in seeking work and food, and to maintain ties with kin who had moved across the previously porous borders of their homelands. When the colonial frontiers were drawn, Western countries attempted to obtain a monopoly on the recruitment of labor in many African countries, which altered the practical and institutional context in which the old migration patterns had been followed, and some might argue, are still followed today. The frontiers were particularly porous for the physical movement of migrants, and people living in borderlands easily maintained transnational cultural and social networks.
Regulated borders
Regulated borders have varying degrees of control on the movement of persons and trade between nations and jurisdictions. Most industrialized nations have regulations on entry and require one or more of the following procedures: visa check, passport check or customs checks. Most regulated borders have regulations on immigration, types of wildlife and plants, and illegal objects such as drugs or weapons. Overall border regulations are placed by national and local governments and can vary depending on nation and current political or economic conditions. Some of the most regulated borders in the world include: Australia, the United States, Israel, Canada, the United Kingdom, and the United Arab Emirates. These nations have government-controlled border agencies and organizations that enforce border regulation policies on and within their borders.
Open borders
An open border is the deregulation and or lack of regulation on the movement of persons between nations and jurisdictions. This definition does not apply to trade or movement between privately owned land areas. Most nations have open borders for travel within their nation of travel, though more authoritarian states may limit the freedom of internal movement of its citizens, as for example in the former USSR. However, only a handful of nations have deregulated open borders with other nations, an example of this being European countries under the Schengen Agreement or the open Belarus-Russia border. Open borders used to be very common amongst all nations, however this became less common after the First World War, which led to the regulation of open borders, making them less common and no longer feasible for most industrialized nations. An example of Open orders include the Schengen Area where 29 European nations mutually abolished their border control.
Demilitarized zones
A demilitarized zone (DMZ) is a border separating two or more nations, groups or militaries that have agreed to prohibit the use of military activity or force within the border's bounds. A DMZ can act as a war boundary, ceasefire line, wildlife preserve, or a de facto international border. An example of a demilitarized international border is the 38th parallel between North and South Korea. The Korean demilitarized zone acts as a safe space for endangered species like the Asiatic black bears, yellow marten, deer, otters and others species; it has been called a rare haven for species at risk of being lost. Other notable DMZ zones include Antarctica and outer space (consisting of all space 100 miles away from the earth's surface), both are preserved for world research and exploration. The prohibition of control by nations can make a DMZ unexposed to human influence and thus developed into a natural border or wildlife preserve, such as on the Korean Demilitarized Zone, the Vietnamese Demilitarized Zone, and the Green Line in Cyprus.
Border economics
Borders undermine economic activity and development by reducing trade activity.
The presence of borders often fosters certain economic features or anomalies. Wherever two jurisdictions come into contact, special economic opportunities arise for border trade. Smuggling provides a classic case; contrariwise, a border region may flourish on the provision of excise or of import–export services — legal or quasi-legal, corrupt or legitimate. Different regulations on either side of a border may encourage services to position themselves at or near that border: thus the provision of pornography, of prostitution, of alcohol, fireworks, and/or of narcotics may cluster around borders, city limits, county lines, ports and airports. In a more planned and official context, Special Economic Zones (SEZs) often tend to cluster near borders or ports.
Even if the goods are not perceived to be undesirable, states will still seek to document and regulate the cross-border trade in order to collect tariffs and benefit from foreign currency exchange revenues. Thus, there is the concept unofficial trade in goods otherwise legal; for example, the cross-border trade in livestock by pastoralists in the Horn of Africa. Ethiopia sells an estimated $250 to $300 million of livestock to Somalia, Kenya and Djibouti every year unofficially, over 100 times the official estimate.
Human economic traffic across borders (apart from kidnapping) may involve mass commuting between workplaces and residential settlements. The removal of internal barriers to commerce, as in France after the French Revolution or in Europe since the 1940s, de-emphasizes border-based economic activity and fosters free trade. Euroregions are similar official structures built around commuting across boundary.
Politics
Political borders have a variety of meanings for those whom they affect. Many borders in the world have checkpoints where border control agents inspect persons and/or goods crossing the boundary.
Some borders require presentation of legal paperwork like passports and visas, or other identity documents, for persons to cross borders. To stay or work within a country's borders aliens (foreign persons) may need special immigration documents or permits; but possession of such documents does not guarantee that the person should be allowed to cross the border.
Moving goods across a border often requires the payment of excise tax, often collected by customs officials. Animals (and occasionally humans) moving across borders may need to go into quarantine to prevent the spread of exotic infectious diseases. Most countries prohibit carrying illegal drugs or endangered animals across their borders. Moving goods, animals, or people illegally across a border, without declaring them or seeking permission, or deliberately evading official inspection, constitutes smuggling. Controls on car liability insurance validity and other formalities may also take place.
A border may have been:
Agreed by the countries on both sides
Imposed by the country on one side
Imposed by third parties, e.g. an international conference
Inherited from a former state, colonial power or aristocratic territory