Dual monarchy
Castile and Aragón from the union of 1469 resulting from the marriage of Ferdinand II of Aragon and Isabella of Castile until the abolition of the Crown of Aragón by the Nueva Planta decrees in 1707. The Kingdom of Spain technically existed as a dual monarchy for 238 years and, for this reason, American history lessons about Spain at the time of the voyages of Christopher Columbus teach not simply about "King Ferdinand," but about "Ferdinand and Isabella."