Political borders do not always follow natural boundaries such as rivers, mountains and seas. Sometimes they divide homogeneous ethnic groups and they can even divide settlements. There are many examples around the world where a single large urban area is found in two countries. In some cases, the political boundary existed before the settlement grew, with people choosing to build a city divided between two counties. On the other hand, there are examples of cities and towns which were divided due to some war or post war agreements.
Divided CapitalsThe Vatican City has been an independent country in the center of Rome, the capital of the Italian Republic, since February 11, 1929 (due to the Lateran Treaty). That actually splits the ancient city of Rome into two capital cities of two modern countries. There are no material boundaries that isolate each part; only politically within the core of Rome there are 0.44 sq km (109 acres) that are a different country. Therefore one city, Rome, is shared between two countries.
Another example of a divided capital city is Nicosia in Cyprus. The so called Green Line has divided the city since the Turkish invasion of 1974. Even though there is no international recognition for Northern Cyprus* as an independent state, the northern part of the island and a portion of Nicosia are not politically controlled by the southern Republic of Cyprus. This actually makes the capital city fragmented.
The case of Jerusalem is quite intriguing. From 1948 (when the State of Israel gained independence) to 1967 (the Six-Day War), parts of the city were controlled by the Kingdom of Jordan and then in 1967 the these parts were reunited with the Israeli parts. If in the future Palestine becomes an independent country with borders that include parts of the Jerusalem, this will be a third example of a divided capital city in the modern world. Nowadays, there are some parts of Jerusalem within the Palestinian West Bank. Currently, the West Bank has an autonomous status within the borders of the State of Israel, so there is no real international division.
Divided Cities in EuropeGermany was the epicenter of many wars in 19th and 20th centuries. That is why this is a country with numerous disunited settlements. It seems that Poland and Germany are the countries that have the biggest number of divided cities. To name a few pairs: Guben (Ger) and Gubin (Pol), Görlitz (Ger) and Zgorzelec (Pol), Forst (Ger) and Zasieki (Pol), Frankfurt am Oder (Ger) and Słubice (Pol), Bad Muskau (Ger) and Łęknica (Pol), Küstrin-Kietz (Ger) and Kostrzyn nad Odrą (Pol). In addition, Germany 'shares' cities with some other neighbouring countries. The German Herzogenrath and the Dutch Kerkrade have been separated since the Vienna Congress of 1815. Laufenburg and Rheinfelfen are divided between Germany and Switzerland.
In the Baltic Sea region, the Estonian city of Narva is separated from the Russian Ivangorod. Estonia also shares the city of Valga with Latvia where it is known as Valka. The Scandinavian countries Sweden and Finland use the Torne River as a natural border. Near the river mouth the Swedish Haparanda is an immediate neighbour of the Finish Torneo. The 1843 Treaty of Maastricht framed the exact border between Belgium and the Netherlands and also determined the separation of a settlement into two parts: Baarle-Nassau (Dutch) and Baarle-Hertog (Belgian).
The city of Kosovska Mitrovica became quite famous in recent years. The settlement was initially divided between the Serbs and the Albanians during the Kosovo war of 1999. After the self-declared independence of Kosovo, the Serbian part is a kind of enclave economically and politically connected to Republic of Serbia.
World War IAfter the end of the World War I four empires (Ottoman Empire, German Empire, Austro-Hungarian Empire, and Russian Empire) in Europe collapsed forming several new independent countries. Ethnic borders were not the primary deciding factors when the new borders were drawn on the political map. That is why numerous villages and towns in Europe were just divided between the freshly established countries. In Central Europe the Polish town Cieszyn and Czech town Český Těšín were divided in the 1920s after the end of the war. As another consequence of this process, the Slovak city Komarno and the Hungarian city Komárom also became politically separated though they had previously been one settlement in the past.
The postwar treaties enabled the urban fragmentation between Czech Republic and Austria where in accordance to the Saint-Germain peace treaty of 1918, the city of Gmünd in Lower Austria was divided and the Czech portion was named České Velenice. Also divided as a result of these treaties were Bad Radkersburg (Austria) and Gornja Radgona (Slovenia).
Divided Cities in the Middle East and AfricaOutside of Europe there are also a few examples of divided cities. In the Middle East there are several examples. In North Sinai, the city of Rafah has two sides: the eastern side is a part of the Palestinian autonomous region of Gaza and the western is known as Egyptian Rafah, a part of Egypt. On the Hasbani River between Israel and Lebanon the settlement Ghajar is politically divided. The Ottoman city of Resuleyn nowadays is split between Turkey (Ceylanpınar) and Syria (Ra's al-'Ayn).
In East Africa the city of Moyale, divided between Ethiopia and Kenya, is the the most significant example of a trans-border settlement.
Divided Cities in the United StatesThe United States has two internationally 'shared' cities. Sault Ste. Marie in Michigan was separated from Sault Ste. Marie in Ontario in 1817 when the UK/US Boundary Commission finalized the procedure for dividing Michigan and Canada. El Paso del Norte was separated in two parts in 1848 as result of the Mexican-American War (Treaty of Guadalupe Hidalgo). The US modern city in Texas is known as El Paso and the Mexican one as Ciudad Juárez.
Within the United States there are also several examples of cross-border cities like Indiana's Union City and Ohio's Union City; Texarkana, found on the border of Texas and Texarkana, Arkansas;, and Bristol, Tennessee and Bristol, Virginia. There are also Kansas City, Kansas, and Kansas City, Missouri.
Divided Cities In the PastMany cities were divided in the past but today they are reunited. Berlin was both in communist East Germany and capitalist West Germany. After the collapse of Nazi Germany in 1945, the country was split into four postwar sectors controlled by the US, the UK, the USSR and France. This division was replicated in the capital city Berlin. Once the Cold War began, the tension between the Soviet portion and the others arose. Initially, the boundary between the parts was not so difficult to cross, but when the number of runaways increased the communist government in the eastern part ordered a stronger form of protection. This was the birth of the notorious Berlin Wall, begun on August 13, 1961. The 155 km long barrier existed till November 1989, when it practically stopped functioning as a border and was broken down. Thus another divided capital city crumbled.
Beirut, the capital of Lebanon, had two independent parts during the Civil War of 1975-1990. The Lebanese Christians were controlling the eastern part and the Lebanese Muslims the western part. The cultural and economic center of the city at that time was a devastated, no-man's land district known as the Green Line Zone. More than 60,000 people died only in the first two years of the conflict. In addition to this, some parts of the city were besieged by either Syrian or Israeli troops. Beirut was reunited and recovered after the end of the bloody war, and today is one of the most prosperous cities in the Middle East.
* Only Turkey recognises the independence of the self-proclaimed Turkish Republic of Northern Cyprus.