Term with which the married couple Isabel I (1451-1504) of Castile and Fernando II of Aragon (1452-1516), kings of the Crown of Castile and Aragon respectively, were designated from the year 1475 after it ended the warlike conflict of the Succession of Castile between the years 1475 and 1479, the title of Catholics was granted to them as a concession by Pope Alexander VI in the year 1494 and which was inherited to their monarchical heirs. Their marriage meant for the first time the union of their crowns, which were also inherited to their successors and which would eventually give rise to the Spanish Monarchy.
Despite the union of these two kingdoms, the institutions belonging to each of them continued to be independent of each other, which would end up changing when, in the 19th century, Spain became a national state. Meanwhile the Kings were at pains to unify so all the Iberian Peninsula using this tool marriage among the princes of Portugal and his sons, actions that are not paid off for early deaths. For its part, the territory of the Muslims in the peninsula ended up being reconquered thanks to the War of Granada, thus integrating the Nasrid kingdom to the Crown of Castile, after this they focused on extending their kingdom by promoting the conquest of areas of North Africa, resulting in obtaining the Canary Islands and other territories. In addition to this, it should be noted that it was the Catholic kings who provided support to Christopher Columbus to seek new routes to the Asian continent, which would end up resulting in the discovery of the New World.
Some of the most important decisions during his tenure were to reduce the resources of the nobility, the maestrazgos were included as part of the crown, part of the authority was taken away from the court, the positions of corregidores were created with the In order to maintain order in the municipalities, they imposed greater control on the armies, decided to expel the Jews who refused to convert to Christianity and in the same way it was done with the Muslims. For his part, with regard to the international arena, his reign was marked by disputes with France.
