Diarchy

Diarchy (from Greek δι-, di-, "double", and -αρχία, -arkhía, "ruled"), 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 (king) and the Ndlovukati (Queen mother) respectively; Nicaragua, which has been led by two co-presidents (who are also husband and wife) since a constitutional amendment in 2025; and San Marino, which is led by two Captains Regent.

Andorra is a parliamentary co-principality. Its princes are (ex officio) 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.

The monarchy of Eswatini is traditionally headed by a male and a female monarch, the Ngwenyama (King, lit. 'lion') and the Ndlovukati (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 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.

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.

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.