The Catholic Monarchs and the Unification of Spain

The Marriage of Isabella and Ferdinand

In 1469, a marriage took place between Isabella I (the future Queen of Castile) and Ferdinand II (the future King of Aragon). Isabella was 18 and Ferdinand was 17. While it was primarily a political marriage, it was also strategic: Ferdinand of Aragon helped secure Isabella's position as the likely Queen of Castile, as she was the sister of the weak King Henry IV.

The Succession Crisis and Civil War

Henry IV had a daughter, Joanna, though it was rumored she was not his biological child but rather the daughter of a palace adviser, Beltrán de la Cueva (hence she was nicknamed La Beltraneja). Upon the death of Henry IV of Castile, a civil war broke out between the supporters of Joanna and those of Isabella. If Joanna had been recognized as the legitimate heir, she would have prevailed, but the situation was unclear. Ultimately, Isabella won the war and, from 1474, became the Queen of Castile.

The Dynastic Union of Castile and Aragon

In 1479, John II, King of Aragon, died, and his son Ferdinand became the King of the Aragonese Crown. This united the crowns of Castile and Aragon under the Trastámara dynasty, ten years after their marriage. This union gave rise to a new political entity: the Spanish Monarchy. This reign marked the transition from the medieval world to the modern era in Spain. Each kingdom maintained its own laws and institutions, forming a plural rather than a unitary state, integrated by Castile and Aragon. While they shared the same monarchy, other aspects remained separate.

Common Foreign Policy and Institutions

The two crowns shared a common foreign policy, such as the struggle against France over the territories of Roussillon and Cerdanya, and the campaigns in Italy involving Sicily, Naples, and Sardinia.

• From an institutional perspective, both crowns kept their own government bodies. Their only common institution was the Inquisition (or Holy Office), an ecclesiastical court tasked with safeguarding the Catholic faith.
• Laws, currency, weights, measures, and languages remained different.
• The tax collection systems were also distinct.
• Legally, subjects of one crown were considered foreigners in the other.

The Three Goals of the Political Union

This political union addressed three common goals for the two crowns:

• Mainland domain
• Religious unity of their subjects
• Centralization of power

The Rise of Authoritarian Monarchy

The Catholic Monarchs established an authoritarian monarchy to reduce the power of the nobility, as both kingdoms had previously faced revolts against royal authority. Consequently, the Castilian Cortes lost significance and were rarely convened. Compared to previous monarchs, the Catholic Monarchs wielded significantly more power.