Reyes Católicos refers to the Catholic Monarchs, Isabella I of Castile and Ferdinand II of Aragon, who ruled Spain jointly in the late 15th century.

The dynastic union of the Crown of Castile and the Crown of Aragon, established by the Catholic Monarchs, created a politically authoritarian system known as the Spanish monarchy. During this time, the Spanish king governed all his territories through a unitary system of councils, but his rule varied from region to region as each had its own unique administration and legal composition. The unity did not necessarily imply uniformity.

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