Dual monarchy occurs when two separate kingdoms are ruled by the same monarch, follow the same foreign policy, exist in a customs union with each other and have a combined military but are otherwise self-governing. The term is typically used to refer to Austria–Hungary, a dual monarchy that existed from 1867 to 1918.
In the 1870s, using the Dual Monarchy of Austria–Hungary as a model, the Prince of Wales (later King Edward VII) and William Ewart Gladstone proposed that Ireland and Great Britain form a dual monarchy. Their efforts were unsuccessful, but the idea was later used in 1904 by Arthur Griffith in his seminal work, The Resurrection of Hungary. Griffith noted how in 1867 Hungary went from being part of the Austrian Empire to a separate co-equal kingdom in Austria-Hungary. Though not a monarchist himself, Griffith advocated such an approach for the Anglo-Irish relationship. The idea was not embraced by other Irish political leaders, and Ireland eventually fought a war of independence to leave the Union of Great Britain and Ireland and form a separate state, the Irish Free State, 1916-1922.
Later historians have used the term to refer to other examples where one king ruled two states, such as Henry V and Henry VI, who were effectively kings of both England and France in the fifteenth century as a result of the formation of a puppet state in a large area of France during the Hundred Years' War, and Denmark–Norway, a dual monarchy that existed from 1536 to 1814.
A dual monarchy is not necessarily a personal union. In a personal union two or more kingdoms are ruled by the same person but there are no other shared government structures. States in personal union with each other have separate militaries, separate foreign policies and separate customs duties. In this sense Austria–Hungary was not a mere personal union, as both states shared a cabinet that governed foreign policy, the Army and common finances.
- Iberian Union (1580-1640)
- Matthew, H. C. G.; Harrison, B. (September 2004; online edn. May 2006), "Edward VII (1841–1910)", Oxford Dictionary of National Biography (Oxford University Press), doi:10.1093/ref:odnb/32975, retrieved 208-11-24 (Subscription required)
- Saul, Nigel (May 1986), "Henry V and the Dual Monarchy", History Today 36 (5): 39–43
- McKenna, J.W. (1965), "Henry VI of England and the Dual Monarchy: Aspects of Royal Political Propaganda, 1422–1432", Journal of the Warburg and Courtauld Institutes 28: 145–162, doi:10.2307/750667, JSTOR 750667
- Slagstad, Rune (2004), "Shifting Knowledge Regimes: the Metamorphoses of Norwegian Reformism", Thesis Eleven 77 (1): 65–83, doi:10.1177/0725513604044236
- Columbia encyclopedia http://www.bartleby.com/65/au/AustroHu.html