List of sets of four countries that border one another

This is a list of sets of at least four countries that border one another. According to four colour theorem, in geometric 2d-space, no more than four continuous two-dimensional shapes can all share one-dimensional boundaries with each other. There are three ways this is possible: three shapes that border one another combining to form an enclave within the fourth (figure 1), a single shape forming an enclave within the combination of three shapes that border one another (figure 2), or two shapes enclaved within the combination of two others (figure 3).

Since, because of exclaves such as overseas territories, not all nations can be represented by single continuous two-dimensional shapes, the number of nations which can possibly share a border with each other is not necessarily limited to four.

Current instances internationally

In typical cases geographically, a set of four countries that border one another is formed when three nations that border one another form a ring around a landlocked fourth (which borders only the other three), as per figure 2. Paraguay, Luxembourg, Burundi, and Malawi are examples of nations that are at the center of such configurations. However, the fact that a country may have exclaves and dependent territories creates other possibilities. As of the 2006 breakup of the State Union of Serbia and Montenegro, there are at least twelve four-nation sets in the world in which each nation shares a boundary (land or fresh water) with each other.

outh America

Paraguay-Brazil-Argentina-Bolivia

This set has existed since the early 19th century. In the 1800s all that existed was the Spanish Viceroyalty of the Río de la Plata and the Portuguese colony of Brazil. With the independence of Argentina (first declared 1810, fully achieved 1816) and Paraguay (1811) the four-border set began to emerge, and was consolidated by the Brazilian and Bolivian independence (1822 and 1825, respectively).

Belarus-Poland-Russia-Ukraine

This set has existed since the 1991 Dissolution of the Soviet Union.

The Russian Kaliningrad Oblast, an exclave on the Baltic Sea, creates a Russian border with Poland.

Balkans

Bosnia and Herzegovina-Serbia-Montenegro-Croatia

This set has existed since the 2006 independence of Montenegro.

Bosnia and Herzegovina has 20 km of coastline on the Adriatic Sea while Croatia borders Montenegro only through the non-contiguous southern portion of the Dubrovačko-neretvanska county, which is technically an exclave, though is connected to the rest of Croatia by territorial waters.

Africa

Burundi-Rwanda-Tanzania-Democratic Republic of the Congo

This set has existed since the 1962 change of the united Belgian colony of Ruanda-Urundi into the independent states of Burundi and Rwanda. Congo had achieved independence in 1960 and was followed the next year by Tanganyika, which would later merge with Zanzibar to form Tanzania. The border between DR Congo and Tanzania is entirely aquatic; the two nations are separated by Lake Tanganyika.

Near misses

*The 40km border between China's Xinjiang Autonomous Region and Russia's Altai Republic prevents Mongolia, Kazakhstan, Russia, and the People's Republic of China from forming a set of four countries that border one another.

*The short border between Sikkim in India and Tibet in the People's Republic of China prevents the group Bhutan, India, Nepal and the People's Republic of China from forming such a set.

*The 2km border between Zambia and Botswana at Africa's "four corners" is all that prevents the group Botswana-Namibia-Zimbabwe-South Africa from satisfying the criteria of four nations that border one another (see International quadripoints for more information).

Former border sets of at least four countries

The first two sets below include boundaries shared by former colonial empires (specifically territorial claims in South America, Africa, India, Europe, and the East and West Indies), and thus do not reflect continuous areas of land.

ee also

* Four colour theorem
* List of land border lengths
* List of political and geographic borders
* List of countries that border only one other country
* List of national border changes since World War I
* List of island nations
* List of divided islands
* Landlocked
* Enclave
* List of enclaves and exclaves
* Foreign Enclaves in China
* Island country
* Quadripoint

Notes

Sources

*CIA World Factbook [https://www.cia.gov/library/publications// CIA World Factbook] (public domain)