Diarch

A diarchy (from Greek , di-, "double", and , -arkhía, "ruled") or duumvirate (from Latin , "the office of the two men") is a form of government characterized by corule, with two people ruling a polity together either lawfully or 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 of 1919 and 1935 which devolved some powers to local councils which had included native Indian representation since 1892. 'Duumvirate' principally referred to the offices of the various duumvirs 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 Sparta's joint kingdom, Rome's consuls, and 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 ranks of the Incan Empire. Modern examples of diarchies are Andorra, whose princes are the President of France and the Bishop of Urgell in Spain; San Marino, whose republic is led by two Captains Regent; and Swaziland, where sovereignty rests jointly in the king and his mother.

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