boundaries, natural

GOVERNMENTS USE physical features as boundaries of political units: boundaries of countries, states, counties, cities, and so forth. (Not all political boundaries follow natural features. A boundary can be geometric, meaning it is be composed of straight-line segments and arcs. There is a cultural type of boundary, as well. This boundary usually separates different ethnic groupings. There are also historical boundaries, which are natural, geometric, and cultural relicts of former political entities.) A natural feature, such as a river or mountain range, is a logical choice, as it is visible and tends to interfere with human movement and interaction. Natural features as political boundaries have advantages and disadvantages for various reasons that we will examine in the next section.

A second type of natural boundary—the boundary of a natural region—separates areas with certain distinctive types of landforms, climates, ecosystems, and so on. Geographers and other scholars often study landscapes within the confines of natural regions, so their boundaries are important. In the early 20th century, geographers and political ideologists merged the boundary of the natural region with the political theory of the organic state. The idea of an organic state with “natural” boundaries influenced Adolf Hitler's dictatorship of GERMANY.

boundaries, natural


When a political boundary conforms to some feature of the physical landscape—a stream, sea, mountain, desert, watershed, lake, marsh, and so forth—it is a natural boundary. Natural features have dimensions of length and breadth, whereas political boundaries are lines of separation. Consequently, two countries that share a natural boundary must agree on a method of marking a boundary line.

Across open land, such as along the crest of a mountain range, a mere line of poles, stones, or cement markers usually suffices. Buoys mark the boundary line if it passes along or across a large lake. Small lakes and narrow rivers may not have any clear demarcation, unless the boundary follows the water's edge. Boundary lines that use physical features are often difficult to survey. Several boundary commissions may be required to work at the setting up boundaries, employing detailed surveying and mapping information, before the involved states are satisfied.


Frontiers often function as natural boundaries. Frontiers are vast unsettled or underpopulated areas that separate and protect countries from each other. The inhospitable nature of frontiers impedes governmental control. Examples of frontiers are expansive deserts, marshes, oceans, frigid lands, dense forests, and rugged mountains. The spread of control from a country's political core area into a frontier gradually eliminates its boundary function.

CHILE is an example of a country that developed while surrounded by frontiers. Chile's political core was in Santiago Valley; the Atacama Desert lay to the north, mountainous ANDES to the east, frigid land to the south, and the PACIFIC OCEAN to the west. From Santiago Valley, the government extended its hegemony into the northern and southern frontiers. The Andes Mountains are a remaining frontier, as they still function as a natural boundary between Chile and ARGENTINA due to their awesome physical presence.

Historically, countries chose natural boundaries for their defensibility against attack from their neighbors. Modern military technology has reduced the defensive function of mountains today. The only exceptions tend to be the more rugged mountainous areas, where military advantage shifts toward controlling summits and key passes that are more defendable. The HIMALAYAS between INDIA and CHINA and the aforementioned Andes between Chile and Argentina are outstanding examples of defendable mountain boundaries.

Regardless of the decline in defensibility of natural boundaries, they remain part of the international political map. In many instances, historical and legal precedence preserve their usage. In other cases, such boundaries are still valuable for their barrier effect: They reduce the potential amount of friction brought on by past hostilities, as well as smuggling or illegal immigration.


Rivers play a dual and contradictory role in the political state. Since the earliest civilizations, some rivers have united people more than they separated them. In early Mesopotamia, the Tigris and Euphrates rivers were highways of internal trade, commerce, and communication. Ease of transportation was crucial when riverine states in this region were in the process of formation, for this, in no small degree influences the extent of the political domain. The same was also true of the NILE in early EGYPT. The RHINE (in Europe), and the MISSISSIPPI (in the UNITED STATES), IRRAWADDY (in MYANMAR), Menam Chao Phraya (in THAILAND), Mekong (in VIETNAM and CAMBODIA), and Hwang Ho (in CHINA) play key roles as national unifiers today.

About one-fifth of the world's political boundaries are rivers. The actual boundary lines of rivers follow along either a bank or the mid-channel of a stream. Most river boundaries are of the mid-channel type in order to assure shared usage by adjoining political units. Lakes, for the same reason, tend to have divisional boundaries. The Canada-U.S. boundary divides the Great Lakes and the CALIFORNIANEVADA boundary does the same for Lake Tahoe. The CASPIAN SEA (actually a lake) in Central Asia, Lake VICTORIA in Africa, and the Bodensee (Lake Constance) in the ALPS are prominent international lakes.

Rivers in particular do not make perfect boundaries. They give the illusion of permanence on a map— a trait valued by boundary makers—but stream courses do change. For instance, the Mississippi, which for most of its length is a U.S. interstate boundary line, has varied its course frequently, leaving parts of the left bank on the right side of the line and vice versa.

The international wanderings of the RIO GRANDE have made the problem of unstable river courses famous. An 1853 survey drew the boundary between the U.S. state of TEXAS and MEXICO down the middle of the Rio Grande. The first of a series of disputes came in the wake of floods in 1864, which caused a change in the river's course that left a chunk of 630 acres (about 1 square mi or 2.6 square km) of land north of the river. Several other wanderings resulted in loses or gains of land for both countries in the ensuing years. As the region became more populated, control of the boundary was more difficult.

In 1884, the two countries agreed that the boundary should follow the abandoned river channel whenever the river changed course. This meant that the area transferred from one bank to the other would remain under the sovereignty of the original state. However, this policy diminished the function of the river as a boundary. In 1905, in order to protect the integrity of the river as the boundary, the governments agreed to exchange land cutoff by the river, but only if the land area or the number of people living there was sufficiently large. Otherwise, the river channel would remain the boundary. A permanent commission was also set up to determine exchanges.

In the 1960s, the two governments finally stabilized the channel with concrete. Land claim problems along the border are rare today. The stabilization of the rivers like the Rio Grande is exceptional. Around the world, meandering rivers create potential boundary problems such as the Rio Grande did. Other disputes evolve around repositioning boundaries so that rivers become boundaries. The list below contains examples of rivers and lakes that are the bases of recent boundary disputes.


Like rivers, mountainous areas may bring together a population, as in the northern Andes (COLOMBIA, Venezuela, Peru, and Ecuador), where heat and humidity drive people to the uplands. As mentioned earlier, historically, governments have held certain mountainous borders in high esteem, because as barriers, they defend a country by holding back or at least slowing down the enemy because of rugged terrain. Such borders are high, rugged, snow-covered, and glaciated and therefore, natural barriers to movement and communication.

Mountains are not ideal places to demarcate boundaries. Surveys may define the boundary along the highest crests (summits), the watershed (or divide), or points along the base of slopes. Additionally, boundary commissions have drawn many such lines after settlement of a mountainous region has already taken place, thereby separating people who share the same language or popular loyalties. A famous example of boundary superimposition happened after World War I. A postwar boundary commission had the task of carving out new countries from a defunct  Germanspeaking Austro-Hungarian Empire. The commissioners drew the new southern border of AUSTRIA assiduously along the high mountain crest of the ALPS.

However, the line divided German speakers in the Alps's Tyrol region into two separate provinces. North Tyrol became part of Austria and South Tyrol part of ITALY. A similar problem of ethnic truncation arose in the Carpathian Mountains between POLAND and CZECHOSLOVAKIA. To the consternation of the people affected, the boundary commissioners did not rectify either problem; they claimed that the coincidence of high mountain crests with the parting of waters and the defensibility of the crests made perfect borders.

Disputes over mountain boundaries can lead countries to the brink of war. For instance, Argentina and Chile prepared for war in the late 19th century, as both countries were dissatisfied with the Andean boundary they shared. At first glance, the Andes Mountains form what seems to be an ideal natural boundary separating the two countries. Unfortunately, a line joining the highest summits of the mountains does not always divide the watersheds. Particularly in the southern part of the boundary, where glaciers in Chile have eroded back the high ends of valleys to a point where they were well to the east of the line connecting the highest summits. Argentines argued that the highest summit line should cut across such valleys, meaning that eastern (high) ends of the valleys should belong to Argentina. Chileans saw it differently. They argued that the line should follow the drainage divide, meaning the boundary should loop around the high ends of the valleys, not pass from peak to peak straight across the valleys. Therefore, Chileans reasoned that the valleys should belong to Chile in their entirety. Ultimately the two countries agreed to ask the Queen of England to settle the dispute. The two countries agreed to a resolution in 1902. In gratitude for averting the war, the peoples of the two countries built a 26-foot-tall bronze Christ of the Andes statue in Uspallata Pass, the main route through the mountains between Buenos Aires and central Chile.


Improved navigation of the seas brought about a concern for the legal status of the oceans and the ownership of marine resources in the 1600s. In 1672, the British claimed marginal waters as far as a cannon could hurl projectiles. Such a range was about 3 nautical mi (5.6 km). A judge of the Supreme Court of Holland added international credence to the distance in 1703, when he ruled that the same distance should be the legal limit of the territorial sea of all coastal countries.

The 3-mile limit remained the standard for most nations and the League of Nations formally accepted it in 1930. After World War II, as states turned increasingly to the seas for their resources as well as their transport and strategic value, international acceptance of the 3-mile limit began to unravel. A series of postwar treaties led to the 1982 United Nations Convention of the Law of the Sea (or Law of the Sea Treaty). Almost all the nations of the world have signed the 1982 convention. Nations view the Law of the Sea Treaty as generally reflecting customary international law, even by countries that have not signed it. The important points of the agreement can be summarized as follows:

Territorial sea. A coastal state's territorial sea can extend to 12 nautical mi (22 kilometers) from the shoreline. The state has full sovereignty rights to the air space above and to all resources in the sea, including those in the underlying seabed and subsoil. The coastal state controls access to the territorial sea by foreign nations. (Some nations, including Peru, Ecuador, SOMALIA, and the PHILIPPINES still claim territorial seas to 200 nautical mi despite the treaty.)

Contiguous zone. A coastal state may extend its legal right to control foreign vessels in a zone that is contiguous to its territorial sea. This zone can be up to 12 nautical mi (22 km) wide. As in the territorial sea, the country's customs and military agencies, as part of their regular duties, can authorize law enforcement personnel to board foreign vessels to search for and seize contraband (for example, illegal drugs or terrorists) or evidence of other alleged illegal activities.

Exclusive economic zone (EEZ). This zone normally extends out from the territorial sea to 200 nautical mi (370 km). However, the zone can extend as far as 350 nautical mi (649 km) to the edge of the continental shelf, if the shelf extends beyond 200 nautical mi. Within its EEZ, the coastal nation has sovereign rights over mineral resources, fishing, and environmental protection. The nation may exercise control over access to the zone for scientific research. It also has control over exploitation of resources, including the mining of minerals, drilling of oil, and the use of water, currents, and winds for the country's production of energy.

The United States has the world's largest EEZ, not because of its coastlines around the contiguous states, but because of the vast additional EEZ area contributed by ALASKA, HAWAII, PUERTO RICO, the U.S. Virgin Islands, and the various U.S. Pacific protectorates and islands, including American Samoa and Guam. As a result, the U.S. EEZ contains many of the world's most productive fisheries, and probably a large share of the mineral wealth of the oceans.

The cooperation of nations to define boundaries in oceans is a necessary and positive step toward avoiding conflicts involving offshore territory and marine resources. Nevertheless, sovereignty disputes over overlapping boundaries of territorial seas and EEZs are increasing political tensions in the world. Most disputes involve overlapping EEZs that surround tiny island nations located on a continental shelf, as such nations can control an EEZ greater than the size of Minnesota. The seas off the coasts of East and Southeast Asia provide many examples of EEZ disputes.


R. Hartshorne (1939) describes how, during the late eighteenth and early nineteenth centuries, European geographers became interested in defining geography as a separate science and not a mere handmaiden of history and government. “In place of the definite areal units of states,” Hartshorne writes, “sharply defined by political boundaries, the new geography required equally definite 'natural' units, somehow defined in nature.”

Geographers produced some interesting studies and maps of natural regions bounded by natural features during the period. Hartshorne makes clear that geographers abandoned the notion that geography was solely the study of natural regions, although he argues that this movement was the genesis of modern physical geography.

The concept of natural regions remains part of the discipline of physical geography. In biogeography, natural boundaries delineate major BIOMEs: forests, grasslands, deserts, tundra, and marine. In geomorphology, natural boundaries define areas of various types of landforms, including expansive plains, plateaus, and mountainous areas. Natural boundaries define the regional limits of numerous other environmental phenomena; they separate climates, vegetation types, soils, geological formations, environmental classifications, and so on.

Unlike boundaries of a political unit, boundaries of a natural region do not have surveyors' monuments to alert us to their locations. It usually takes an informed observer to identify such  boundaries. In addition to geographers, scholars ranging from anthropologists to zoologists, concern themselves with identifying natural boundaries, as they also study plant and wildlife within the confines of natural regions.

A boundary of a natural region is actually a transitional zone that is sometimes difficult to define. For instance, the topographic boundary between the Great Plains and the Rocky Mountains in North America is a gradual change from planar to mountainous terrain. This boundary is an example of a single-feature boundary, as it separates two classes of one element—landforms. Boundaries of multielement regions are more difficult to define, as each element's distribution fails to coincide perfectly with that of the other elements. For example, broadleaf deciduous trees and coniferous trees do not coincide well in a mixed forest biome. As a result, the biome's boundary is a compromise that depends upon the decision of the scientists who are defining the region.


In the late 19th and early 20th centuries, some political geographers treated the state (meaning a country) as if it were a natural region. Friedrich Ratzel was an influential German political geographer who developed this organic state theory. He used an analogy to compare the state with an organism. According to his analogy, a state is a living thing. Like plants and people, it needs living space and resources and constantly competes against other states for them. Hence, state boundaries are natural or organic entities that must grow outward for the state to survive. Strong governments, according to this view, would seek to adjust their natural boundaries by conquest or annexation. Ratzel emphasized that his description was an analogy, not a basis for state policy.

A few scholars of the time—notably the Swedish political scientist Rudolf Kjellen—took Ratzel's analogy literally and insisted flatly that the interdependence of people and land creates an organic state. This socalled theory, as Kjellen saw it, gave countries a rationale to use force to expand their borders to meet their territorial needs. These ideas later expanded in the 1920s by the German Karl Haushofer. The German dictator Adolf Hitler adopted Haushofer's organic state theory wholeheartedly. Hitler called his organic state the Fatherland. The Fatherland, according to Hitler, was composed of Germans, who were an advanced “race” of people whose superiority came from an innate spiritual bond with the land. Before the outbreak of World War II, heavy concentrations of Germans lived in countries adjoining GERMANY. Hitler believed that unifying the superior German race would strengthen the Fatherland, which would then continue to grow its boundaries through armed aggression until it encompassed Europe.

Hitler's persuasive speeches and Nazi propagandists' deceptive maps seduced German citizens into thinking that expanding Germany's borders to include other Germans living in adjoining countries was the right thing to do. Hitler began expanding German territory to its “natural” limits by invading Austria in 1934; this was a country composed entirely of German speakers.

Under the same trumped up pretext, Hitler invaded the Rhineland in France (in 1935), annexed part of Czechoslovakia (1938), and invaded western Poland (1939). All these areas had large German populations. The invasion of Poland precipitated World War II, as most countries of Europe knew Hitler's aggression would not stop in German-populated areas. Italy and JAPAN subsequently used variations of the facile organic state theory to justify their aggressions as well.)

Geographers are not to blame for World War II; they discarded the organic state theory into the dustbin of bad ideas long before the war began. Rather, the blame goes to self-serving demagogues who resurrected, perverted, and used the theory as a rationale for boundary aggression and war. Lamentably, in a culturally diverse modern world, misguided claims to natural-cultural boundaries are always a danger. For example, Bosnia and Herzegovina's leaders, whose population is composed mainly of Serbs, used ideas akin to the organic state theory to justify “ethnic cleansing” and forced emigration of non-Serbian minorities in the 1990s. Only military action by U.S. and North Atlantic Treaty Organization forces was able to stop government-sponsored terror in that country.

A lesson from Hitler's Germany and Bosnia and Herzegovina's “ethnic cleansing” is that country boundaries are not natural and therefore limited to a particular nation or group of people:  Mountains, rivers, lakes, oceans, and cultural lines only become boundaries after people decide that they should be. Indeed, countries have a choice of using fairness and compromise over prejudice and war in dealing with socalled natural boundary disputes.