Diarchy
Diarchy, duarchy, or duumvirate is a form of government characterized by co-rule, with two people ruling a polity together either lawfully or de facto, by collusion and force. The leaders of such a system are usually known as corulers.
Historically, diarchy particularly referred to the system of shared rule in British India established by the Government of India Acts 1919 and 1935, which devolved some powers to local councils, which had included native Indian representation under the Indian Councils Act 1892. 'Duumvirate' principally referred to the offices of the various duumviri established by the Roman Republic. Both, along with less common synonyms such as biarchy and tandemocracy, are now used more generally to refer to any system of joint rule or office. A monarchy temporarily controlled by two or more people is, however, usually distinguished as a coregency.
Corule is one of the oldest forms of government. Historical examples include the Pandyan dynasty of Tamilakam, Sparta's joint kingship, the Roman Republic's consuls, Carthage's Judges, and several ancient Polynesian societies. Systems of inheritance that often led to corule in Germanic and Dacian monarchies may be included as well, as may the dual occupants of the imperial title of the Inca Empire, or its system of succession.
Modern examples of diarchies are Andorra, whose princes are the president of France and the Bishop of Urgell in Catalonia; Eswatini that is jointly headed by a male and a female monarch, the Ngwenyama and the Ndlovukati respectively; Nicaragua, which has been led by two co-presidents since a constitutional amendment in 2025; and San Marino, which is led by two Captains Regent.
Formal use
Current diarchies
Andorra
is a parliamentary co-principality. Its princes are the French president and the bishop of Urgell in Catalonia, Spain. Since 1962, the French president has been elected by universal suffrage within France. The bishop of the diocese of Urgell is appointed by the Roman Catholic pope.Eswatini
The monarchy of Eswatini is traditionally headed by a male and a female monarch, the Ngwenyama and the Ndlovukati respectively. In practice, the Ngwenyama effectively holds power as the executive and administrative head of state; the Ndlovukati's role is spiritual and more symbolic but may act as queen regent in the absence of a king. The functions of both the Ngwenyama and Ndlovukati are established in the constitution in accordance with tradition.Nicaragua
In 2025, during the presidency of Daniel Ortega, the National Assembly approved multiple amendments to the Constitution of Nicaragua that included proclaiming Ortega and his wife, Vice President Rosario Murillo, as co-presidents.Northern Ireland
Under the terms of the 1998 Good Friday Agreement intended to end the conflict in Northern Ireland, the First Minister and deputy First Minister serve as joint heads of the area's executive. Both positions exercise identical executive powers; however they are not heads of state.San Marino
The captains regent of San Marino are elected every six months by the Sammarinese parliament, the Grand and General Council. They serve as joint heads of state, and are normally chosen from opposing parties.Historical diarchies
Sparta
The office of king in ancient Sparta was divided between two kings from separate dynasties, each holding a veto over the other's actions. However, the Spartan kings' powers and duties consisted mainly of leading the Spartan army on campaign and certain religious functions, as well as having ex-officio seats in the Gerousia. Actual day-to-day public administration in Sparta was managed by the ephors.Roman Republic
Following the overthrow of the Roman monarchy, the Romans established an oligarchic Roman Republic which divided supreme executive power between two consuls, both elected each year and each holding a veto over the other's actions.The historical duumviri were not rulers but magistrates, performing various judicial, religious, or public functions.
Kartli
According to the Conversion of Kartli, Leonti Mroveli, Vakhushti Bagrationi, Teimuraz Bagrationi and Pavle Ingorokva, there existed a dual power in Kartli at the time of the kings mentioned below:- Bartom II and Kʽartʽam
- Pʽarsman I and Kaos
- Azork and Armazel
- Amazasp I and Derok
- Pʽarsman II and Mirdat I
Hungary
The Hungarians originally possessed a system of dual kingship, with religious authority vested in the kende and military authority vested in the war-chief. It is believed that when the kende Kurszán was killed a little after the arrival of the Hungarians in Pannonia, his role was usurped by the war-chief Árpád, establishing the Hungarian monarchy. It is not known with certainty whether Árpád was originally the kende or the gyula.Afghanistan
The Ghurid Empire was an established diarchy between Ghiyath al-Din Muhammad and Muhammad of Ghor. The diarchy lasted from 1173 to 1203 until the death of Ghiyath al-Din, leaving his brother, Muhammad sole ruler of the Ghurid empire.Japan
During Japan's shogunate, the emperor was notionally a supreme spiritual and temporal lord who delegated authority for joint rule to the shōgun. In practice, the shōguns power was so complete that they are usually considered de facto monarchs rather than viceroys or corulers.Medieval Europe
A paréage was a feudal treaty recognizing the "equal footing" of two sovereigns over a territory. The most famous such arrangement was the 1278 treaty that established modern Andorra. Others include Maastricht, which was shared by the Duke of Brabant and the Prince-Bishop of Liège. After the establishment of the Dutch Republic, it became a condominium of Liège and the United Provinces, which administered it through the States General of the Netherlands until 1794.Tibet
Between 1642 and 1751, political power in Tibet was shared between the 5th, 6th, and 7th Dalai Lamas who headed the realm's Buddhist state religion and various secular rulers known as desis. The growing power of the desis caused the 7th Dalai Lama to abolish the post and replace it with a council known as the Kashag, permitting him to consolidate his authority over the realm. A similar system arose in Bhutan, with the Wangchuck governor of Trongsa becoming the Druk Desi and Druk Gyalpo in 1907. In contrast to Tibet, the dynasty eventually consolidated its power and now rules as the kings of Bhutan.Russia
From 1619 to 1633, Tsar Michael of Russia ruled alongside his father, Patriarch Filaret of Moscow. Both were addressed as "Великий государь", held court together, and when they did not the ceremony was the same. While both were equal in theory, in practice Patriarch Filaret ruled, with Michael supporting whatever his father ordered.Between the February Revolution in March 1917 and the October Revolution in November, political power in Russia was divided between the Russian Provisional Government and the Petrograd Soviet, a condition described by Vladimir Lenin as "dual power". He elaborated the situation into a dual-power doctrine, whereby communists collaborated with and then supplanted existing bourgeois forms of government.
England, Scotland and Ireland
Although the Kingdoms of England, Scotland and Ireland were monarchies, they became de facto diarchies in personal union during the co-rule of William II and III and Mary II. After the Glorious Revolution deposed James VII and II, his kingships were succeeded in 1689 by his daughter Mary and his son-in-law and nephew William, who jointly ruled England, Scotland and Ireland until Mary died in 1694, succeeded by William as the sole monarch.Canada
The Province of Canada, which existed from 1841 to 1867, was governed by two joint premiers. Usually, one was chosen from the English-speaking Canada West and the other one from the French-speaking Canada East.India
Named as the India Secretary for the Lloyd George ministry, Edwin Samuel Montagu made the "Grand Declaration" on 20 August 1917 that British policy would henceforth be "increasing association of Indians in every branch of the administration and the gradual development of self-governing institutions". Montagu and Viscount Chelmsford, the Governor-General of India, then made an extensive tour of the subcontinent in 1917 and 1918. The Montague–Chelmsford Report's recommendations formed the basis for the Government of India Act 1919 that established "diarchy" in British India.Under that act, the executive was to be headed by a governor appointed by the Secretary of State, who could consult the Governor General. The governor was responsible to the Secretary of State for acts of omission and commission. He was to maintain law and order in the province and ensure that the provincial administration worked smoothly. In respect of transferred subjects, he was to be assisted by his ministers whereas reserved subjects were to be administered by the Governor General and his executive council.
The members of the Executive Council were to be appointed by the Secretary of State and were responsible to him in all matters. There were certain matters that he was to administer at his own discretion, in which he was responsible to the Secretary of State. Each councillor was to remain in office for a period of four years. Their salaries and service conditions were not subject to the vote of provincial legislature. All decisions in the council were to be taken by a majority of votes, the Governor being able to break ties.