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Diarchy (fromGreekδι-,di-, "double",[1] and-αρχία,-arkhía, "ruled"),[2][note 1][3]duarchy,[4] orduumvirate[5][note 2] is a form of government characterized byco-rule, with two people ruling a polity together eitherlawfully orde facto, by collusion and force. The leaders of such a system are usually known ascorulers.[6]
Historically,diarchy particularly referred to the system of shared rule inBritish India[2] established by the Government of India Acts1919 and1935, whichdevolved some powers to local councils, which had included native Indian representation under theIndian Councils Act 1892. 'Duumvirate' principally referred to the offices of the variousduumviri established by theRoman Republic.[5] Both, along with less common synonyms such asbiarchy[7] andtandemocracy,[8][note 3] are now used more generally to refer to any system of joint rule or office. Amonarchy temporarily controlled by two or more people is, however, usually distinguished as acoregency.
Corule is one of the oldest forms of government. Historical examples include thePandyan dynasty ofTamilakam,Sparta'sjoint kingship, theRoman Republic'sconsuls,Carthage'sJudges, and several ancientPolynesian societies. Systems of inheritance that often led to corule inGermanic andDacian monarchies may be included as well, as may the dual occupants of the imperial title of theInca Empire, or its system of succession.[9]
Modern examples of diarchies areAndorra, whose princes are thepresident of France and theBishop of Urgell inCatalonia;Eswatini that is jointly headed by a male and a female monarch, theNgwenyama (king) and theNdlovukati (Queen mother) respectively;Nicaragua, which has been led by twoco-presidents (who are also husband and wife) since a constitutional amendment in 2025; andSan Marino, which is led by twoCaptains Regent.
Andorra is a parliamentary co-principality. Its princes are (ex officio) theFrenchpresident and thebishop of Urgell inCatalonia,Spain. Since 1962, the French president has beenelected byuniversal suffrage withinFrance. The bishop of the diocese of Urgell is appointed by theRoman Catholicpope.[10][11]
The monarchy ofEswatini is traditionally headed by a male and a female monarch, theNgwenyama (King,lit. 'lion') and theNdlovukati (lit. 'she-elephant', usually the mother of the reigning iNgwenyama) 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 asqueen regent in the absence of a king.[12][13] The functions of both the Ngwenyama and Ndlovukati are established in theconstitution in accordance with tradition.[13]
In 2025, during the presidency ofDaniel Ortega, theNational Assembly approved multiple amendments to theConstitution of Nicaragua that included proclaiming Ortega and his wife, Vice PresidentRosario Murillo, as co-presidents.[14]
Under the terms of the 1998Good Friday Agreement intended to end theconflict inNorthern Ireland, theFirst Minister anddeputy First Minister serve as joint heads of the area'sexecutive.[15] Both positions exercise identical executive powers; however they are notheads of state.
Thecaptains regent (Italian:Capitani Reggenti) ofSan Marino are elected every six months by the Sammarinese parliament, theGrand and General Council. They serve as joint heads of state, and are normally chosen from opposing parties.[16]
The office of king inancient Sparta was divided between two kings from separate dynasties, each holding aveto over the other's actions. However, the Spartan kings' powers and duties consisted mainly of leading theSpartan army on campaign (during which only one king would usually lead a given force) and certain religious functions, as well as having ex-officio seats in theGerousia (Senate). Actual day-to-day public administration in Sparta was managed by theephors.
Following theoverthrow of the Roman monarchy, the Romans established anoligarchicRoman Republic which dividedsupreme executive power (Latin:imperium) between twoconsuls, both elected each year and each holding aveto over the other's actions.
The historicalduumviri were not rulers but magistrates, performing various judicial, religious, or public functions.
According to theConversion of Kartli,Leonti Mroveli,Vakhushti Bagrationi,Teimuraz Bagrationi andPavle Ingorokva, there existed a dual power inKartli at the time of the kings mentioned below:
According toCyril Toumanoff, the diarchs ofKartli in 370-378 wereSauromaces II andMihrdat III.
TheHungarians originally possessed a system of dual kingship, with religious authority vested in thekende and military authority vested in thewar-chief (gyula). It is believed that when the kendeKurszán was killedc. 904 a little after the arrival of the Hungarians inPannonia, his role was usurped by the war-chiefÁrpád, establishing the Hungarian monarchy. It is not known with certainty whether Árpád was originally the kende or the gyula.
TheGhurid Empire was an established diarchy betweenGhiyath al-Din Muhammad andMuhammad 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.[18][19]
DuringJapan'sshogunate, theemperor was notionally a supreme spiritual and temporal lord who delegated authority for joint rule to theshōgun. In practice, theshōguns' power was so complete that they are usually consideredde facto monarchs rather thanviceroys or corulers.
Aparéage was afeudal treaty recognizing the "equal footing" (Latin:pari passu) of two sovereigns over a territory. The most famous such arrangement was the1278 treaty that established modernAndorra. Others includeMaastricht, which was shared by theDuke of Brabant and thePrince-Bishop of Liège. After the establishment of theDutch Republic, it became acondominium of Liège and the United Provinces, which administered it through theStates General of the Netherlands until 1794.
Between 1642 and 1751, political power inTibet was shared between the5th,6th, and7th Dalai Lamas who headed the realm's Buddhiststate 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 theKashag, permitting him to consolidate his authority over the realm. A similar system arose inBhutan, with theWangchuckgovernor (penlop) ofTrongsa becoming theDruk Desi andDruk Gyalpo in 1907. In contrast to Tibet, the dynasty eventually consolidated its power and now rules as the kings of Bhutan.
From 1619 to 1633, TsarMichael of Russia ruled alongside his father,Patriarch Filaret of Moscow. Both were addressed as "Великий государь" (velikiy gosudar; "Great Sovereign"), 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.[20]
Between theFebruary Revolution in March 1917 and theOctober Revolution in November, political power in Russia was divided between theRussian Provisional Government and thePetrograd Soviet, a condition described byVladimir Lenin as "dual power". He elaborated the situation into a dual-power doctrine, wherebycommunists collaborated with and then supplanted existing bourgeois forms of government.
Although the Kingdoms ofEngland,Scotland andIreland were monarchies, they becamede facto diarchies inpersonal union during the co-rule ofWilliam II and III andMary II. After theGlorious Revolution deposedJames VII and II, his kingships were succeeded in1689 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.
TheProvince of Canada, which existed from 1841 to 1867, was governed by twojoint premiers. Usually, one was chosen from the English-speakingCanada West and the other one from the French-speakingCanada East.[citation needed]
Named as theIndia Secretary for theLloyd 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 andViscount Chelmsford, theGovernor-General of India, then made an extensive tour of the subcontinent in 1917 and 1918. TheMontague–Chelmsford Report's recommendations formed the basis for theGovernment of India Act 1919 that established "diarchy" inBritish 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.
The 1960 constitution of Western Samoa declared paramount chiefsMalietoa Tanumafili II andTupua Tamasese Meaʻole as jointheads of state when Western Samoa gained independence in 1962. This arrangement ended when Tupua Tamasese died the following year, succeeded by Malietoa as the sole head of state.[21][22]
Following acoup d'état in 1964, formerVice PresidentRené Barrientos rose to power as president of the military junta. The following year, faced with discontent from loyalists of GeneralAlfredo Ovando Candía, Barrientos promulgated the co-presidency between himself and Ovando Candía. The pair ruled as dual presidents until 1966 when Barrientos resigned in order to run in that year'sgeneral election.
After the2019–2021 Israeli political crisis, Israel'sBasic Law: The Government underwent a major change. A system of two prime ministers, appointed at the same time by theKnesset, was established. According to the new method, there was anAlternate Prime Minister of Israel in addition to the standardPrime Minister of Israel. After a half of the government's term, the two prime ministers would change positions as part of arotation government. During the term, the government's roles and duties were divided between the two prime ministers, each one of them entitled to remove ministers without the other's interference.
However, this system did not survive even until the first planned rotation and was abolished again after the formation of thethirty-seventh government of Israel at the end of 2022.
Shared power arrangements within a modern bureaucracy may also be known as a "diarchy" or "duumvirate". Examples include the joint authority of theChief of the Defence Force and the Secretary of the Department of Defence over theAustralian Defence Organisation.
The status of monarchs is sometimes impugned by accusations of corule when an advisor, family member, lover, or friend appears to have taken too great a hand in government.Lü Buwei in Chinese history andFrançois Leclerc du Tremblay in France are famous examples of "éminences grises" who controlled much of their countries' policies. In British history,George VI's reign was mocked as a "split-levelmatriarchy in pants" owing to the supposed influence of his mother,Queen Mary and his wifeQueen Elizabeth.[23]
Owing toConfucian notions offilial piety, Chinese and Japanese emperors were sometimes able to 'retire' but continue to exert great influence over state policy. InIndonesia,Sukarno and his vice presidentMohammad Hatta were nicknamed the Duumvirate (Dwitunggal), with Sukarno setting government policy and rallying support and Hatta managing day-to-day administration. More recently, the great influence ofVladimir Putin over his successorDmitry Medvedev was considered a duumvirate,[24] or tandemocracy (see alsoMedvedev–Putin tandemocracy),[8] until Putin's resumption of the office of president established him as the greater figure.[25]
Within electoral politics, governments, coalitions and parties may sometimes have two fairly equal leaders, as with:
In addition to actual sharing of political power between religious and military leaders, as occurred in Tibet and Bhutan, the greatsoft power of a religious leader such as thePope of theCatholic Church over a devout country can sometimes be described as a form of diarchy or corule.[original research?]
The President of France, Emmanuel Macron, serves as Co-Prince of Andorra in addition to his duties as French President and is one of the few examples of a democratically elected leader serving in a royal capacity in another country. Since 2003, the other Co-Prince is the Catholic Bishop of Urgell from Spain, Joan-Enric Vives i Sicília.
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