A city-state is a sovereign state, also described as a type of small independent country, that usually consists of a single city and its dependent territories. Historically, this included cities such as Rome, Athens, Carthage, and the Italian city-states during the Renaissance. Today only a handful of sovereign city-states exist, with some disagreement as to which are city-states. A great deal of consensus exists that the term properly applies currently to Singapore, Monaco, and Vatican City. City states are also sometimes called micro-states which however also includes other configurations of very small countries.
A number of other small states share similar characteristics, and therefore are sometimes also cited as modern city-states. Namely, Qatar, Brunei, Kuwait, Bahrain, and Malta, which each have an urban center comprising a significant proportion of the population, though all have several distinct settlements and a designated or de facto capital city. Occasionally, other small states with high population densities, such as San Marino, are also cited, despite lacking a large urban centre characteristic of traditional city-states.
Several non-sovereign cities enjoy a high degree of autonomy, and are sometimes considered city-states. Hong Kong and Macau, along with independent members of the United Arab Emirates, most notably Dubai and Abu Dhabi, are often cited as such.
Historical city-states included Sumerian cities such as Uruk and Ur; Ancient Egyptian city-states, such as Thebes and Memphis; the Phoenician cities (such as Tyre and Sidon); the five Philistine city-states; the Berber city-states of the Garamantes; the city-states of ancient Greece (the poleis such as Athens, Sparta, Thebes, and Corinth); the Roman Republic (which grew from a city-state into a great power); the Mayan and other cultures of pre-Columbian Mesoamerica (including cities such as Chichen Itza, Tikal, Copán and Monte Albán); the central Asian cities along the Silk Road; the city-states of the Swahili coast; Venice; Ragusa; states of the medieval Russian lands such as Novgorod and Pskov; and many others. Danish historian Poul Holm has classed the Viking colonial cities in medieval Ireland, most importantly Dublin, as city-states.
Some of the most well-known examples of city-state culture in human history are the ancient Greek city-states and the merchant city-states of Renaissance Italy, which organised themselves as small independent centers. The success of small regional units coexisting as autonomous actors in loose geographical and cultural unity, as in Italy and Greece, often prevented their amalgamation into larger national units. However, such small political entities often survived only for short periods because they lacked the resources to defend themselves against incursions by larger states. Thus they inevitably gave way to larger organisations of society, including the empire and the nation-state.
In the history of mainland Southeast Asia, aristocratic groups, Buddhist leaders, and others organized settlements into autonomous or semi-autonomous city-states. These were referred to as mueang, and were usually related in a tributary relationship now described as mandala or as over-lapping sovereignty, in which smaller city-states paid tribute to larger ones that paid tribute to still larger ones—until reaching the apex in cities like Ayutthaya, Bagan, Bangkok and others that served as centers of Southeast Asian royalty. The system existed until the 19th century, when colonization by European powers, and Thailand's (then known as Siam) resulted in the adoption of the modern concept of statehood.
In early Philippine history, the Barangay was a complex sociopolitical unit which scholars have historically considered the dominant organizational pattern among the various peoples of the Philippine archipelago. These sociopolitical units were sometimes also referred to as Barangay states, but are more properly referred to using the technical term "polity, so they are usually simply called "barangays." Evidence suggests a considerable degree of independence as "City states" ruled by Datu's , Rajahs and Sultan's.  Early chroniclers record that the name evolved from the term balangay, which refers to a plank boat widely used by various cultures of the Philippine archipelago prior to the arrival of European colonizers.
In the Holy Roman Empire the Free Imperial Cities enjoyed a considerable autonomy, buttressed legally by international law following the Peace of Westphalia (1648). Some, like the three Hanseatic cities of Bremen, Hamburg and Lübeck, pooled their economic relations with foreign powers and were able to wield considerable diplomatic clout. After the dissolution of the Holy Roman Empire in 1806, cities – then members of different confederacies – officially became sovereign city-states – such as the Canton of Basel City (1833–48), the Free Hanseatic City of Bremen (1806–11 and again 1813–71), the Free City of Frankfurt upon Main (1815–66), the Canton of Geneva (1813–48), the Free and Hanseatic City of Hamburg (1806–11 and again 1814–71), the Free and Hanseatic City of Lübeck (1806–11 and again 1813–71), and the Free City of Kraków (1815–1846). Under Habsburg rule the city of Fiume had the status of a Corpus separatum, which - while falling short of an independent sovereignty - had many attributes of a city state.
A later city-state, though lacking sovereignty, was West Berlin (1948–1990), being a state legally not belonging to any other state, but ruled by the Western Allies. They allowed – notwithstanding their overlordship as occupant powers – its internal organisation as one state simultaneously being a city, officially called Berlin (West). Though West Berlin maintained close ties to the West German Federal Republic of Germany, it was legally never part of it.
The Free City of Danzig was a semi-autonomous city-state that existed between 1920 and 1939, consisting of the Baltic Sea port of Danzig (now Gdańsk, Poland) and nearly 200 towns in the surrounding areas. It was created on 15 November 1920 under the terms of Article 100 (Section XI of Part III) of the 1919 Treaty of Versailles after the end of World War I.
After a prolonged period where the city of Fiume enjoyed considerable autonomy under Habsburg rule (see Corpus separatum (Fiume), The Free State of Fiume was proclaimed as a fully independent free state which existed between 1920 and 1924. Its territory of 28 km2 (11 sq mi) comprised the city of Fiume (now in Croatia and, since the end of World War II, known as Rijeka) and rural areas to its north, with a corridor to its west connecting it to Italy.
The Shanghai International Settlement (1845–1943) was an international zone with its own legal system, postal service, and currency.
The international zone within the city of Tangier, in North Africa was approximately 373 km2 (144 sq mi). It was at first under the joint administration of France, Spain, and the Great Britain. Which later became Portugal, Italy, Belgium, the Netherlands, Sweden, and the United States. The international zone was initially attached to Morocco. It then became a French-Spanish protectorate from 1923 until the 29 of October 1956 when it was reintegrated into the state of Morocco.
The Klaipėda Region or Memel Territory was defined by the Treaty of Versailles in 1920 when it was put under the administration of the Council of Ambassadors. The Memel Territory was to remain under the control of the League of Nations until a future day when the people of the region would be allowed to vote on whether the land would return to Germany or not. The then predominantly ethnic German Memel Territory (Prussian Lithuanians and Memellanders constituted the other ethnic groups), situated between the river and the town of that name, was occupied by Lithuania in the Klaipėda Revolt of 1923.
The Free Territory of Trieste was an independent territory situated in Central Europe between northern Italy and Yugoslavia, facing the north part of the Adriatic Sea, under direct responsibility of the United Nations Security Council in the aftermath of World War II, from 1947 to 1954. The UN attempted to make the Free Territory of Trieste into a city state, but it never gained real independence and in 1954 its territory was divided between Italy and Yugoslavia.
Under the United Nations Partition Plan for Palestine of 1947, Mandatory Palestine was to be partitioned into three states: a Jewish state of Israel, an Arab state of Palestine, and a Corpus separatum (Latin for "separated body") consisting of a Jerusalem city-state under the control of United Nations Trusteeship Council. Although the plan had some international support and the UN accepted this proposal (and still officially holds the stance that Jerusalem should be held under this regime), implementation of the plan failed as the 1948 Palestine war broke out with the 1947–48 Civil War in Mandatory Palestine, ultimately resulting in Jerusalem being split into West Jerusalem and East Jerusalem. Israel would eventually gain control of East Jerusalem in the Six-Day War in 1967.
The Principality of Monaco is an independent city-state. Monaco-Ville (the ancient fortified city) and Monaco's well-known area Monte Carlo are districts of a continuous urban zone, not distinct cities, though they were three separate municipalities (communes) until 1917. The Principality of Monaco and the city of Monaco (each having specific powers) govern the same territory.
Singapore is an island city-state in Southeast Asia. About 5.2 million people live and work within 700 square kilometres (270 sq mi), making Singapore the 2nd-most-densely populated country in the world after Monaco, another city-state. Singapore was part of Malaysia before it was expelled from the Federation in 1965, becoming an independent republic, a city and a sovereign country. The Economist refers to the nation as the "world’s only fully functioning city-state".
Until 1870, the city of Rome had been controlled by the pope as part of his Papal States. When King Victor Emmanuel II seized the city in 1870, Pope Pius IX refused to recognize the newly formed Kingdom of Italy.
Because he could not travel without effectively acknowledging the authority of the king, Pius IX and his successors each claimed to be a "Prisoner in the Vatican", unable to leave the 0.44 km2 (0.17 sq mi) papal enclave once they had ascended the papal thrones.
The impasse was resolved in 1929 by the Lateran Treaties negotiated by the Italian dictator Benito Mussolini between King Victor Emmanuel III and Pope Pius XI. Under this treaty, the Vatican was recognized as an independent state, with the Pope as its head. The Vatican City State has its own citizenship, diplomatic corps, flag, and postage stamps. With a population of less than 1,000 (mostly clergymen), it is by far the smallest sovereign country in the world.
Some cities or urban areas, while not sovereign states, may nevertheless enjoy such a high degree of autonomy that they function as "city-states" within the context of the sovereign state that they belong to. Historian Mogens Herman Hansen describes this aspect of self-government as: "The city-state is a self-governing, but not necessarily independent political unit."
Two cities in Germany, namely Berlin and Hamburg, are considered city-states (German: Stadtstaaten). Additionally, the state of Bremen is often called a city-state although it consists of the two cities of Bremen and Bremerhaven, which are separated by the state of Lower Saxony. Together with thirteen area states (German: Flächenländer) they form the sixteen federal states of Germany.
Generally, the city-states have no other rights or duties than the other states. Through the financial redistribution system of Equalization Payments in Germany (German: Länderfinanzausgleich), they do receive more money because of their demographic characteristics. The city-states are most distinctive due to the names of their state organs: their governments are called Senate, the prime ministers 'mayor' (Governing Mayor in Berlin and First Mayor in Hamburg) or President of the Senate (in Bremen) and also the expressions for their state parliaments differ from the other states.
In the 18th century many German cities were free imperial cities (German: Reichsstädte), without a principality between them and the imperial level. After the Napoleonic era, in 1815, four were still city-states: Hamburg, Bremen and Lübeck in Northern Germany, and Frankfurt where the Federal Convention was located. Frankfurt was incorporated by Prussia in 1866, and Lübeck became a part of Prussia during the national socialist regime in 1937 (Greater Hamburg Law). After 1945, Berlin was a divided city, and the Western part became a quasi German state under (Western) Allied supervision. Since 1990/1991, the reunited Berlin is an ordinary German state among others.