Ferdinand is considered the de facto first king of Spain, and was described as such during his reign, even though, legally, Castile and Aragon remained two separate kingdoms until they were formally united by the Nueva Planta decrees issued between 1707 and 1716.

The two young monarchs were initially obliged to fight a civil war against Joanna, the purported daughter of Henry IV, and were swiftly successful.

The first years of Ferdinand and Isabella's joint rule saw the Spanish conquest of the Emirate of Granada, the last Islamic al-Andalus entity on the Iberian peninsula, completed in 1492.

1492 was also the year in which the monarchs commissioned Christopher Columbus to find a westward maritime route for access to Asia, which resulted in the Spanish arrival in the Americas.

In 1494 the Treaty of Tordesillas divided the entire world beyond Europe between Portugal and Castile (Spain) for conquest and dominion purposes – by a north–south line drawn down the Atlantic Ocean.

The latter part of Ferdinand's life was largely taken up with disputes with successive kings of France over control of Italy, the Italian Wars.

In 1494, Charles VIII of France invaded Italy and expelled Alfonso II, who was Ferdinand's first cousin once removed and step nephew, from the throne of Naples.

The agreement soon fell apart and, over the next several years, Ferdinand's great general Gonzalo Fernández de Córdoba fought to take Naples from the French, finally succeeding by 1504.

On the day of his wife's death, he formally renounced his title as King of Castile and instead became governor (gobernador) of the kingdom, as a way to become regent.

Ferdinand attempted to retain the regency permanently, but was rebuffed by the Castilian nobility and replaced with Joanna's husband.

But the Treaty of Villafáfila did not hold for long because of the death of Philip; Ferdinand returned as regent of Castile and as "lord of the Indies".

But the infant Prince John died within hours and was buried in the convent of Saint Paul in Valladolid, Kingdom of Castile and Leon, and later transferred to Poblet Monastery, Vimbodí i Poblet, Principality of Catalonia (Crown of Aragon), traditional burial site of the kings of Aragon.

Cardinal Francisco Jiménez de Cisneros, the Chancellor of the Kingdom, was made regent, but the upper nobility reasserted itself.

The Holy League was generally successful in Italy, as well, driving the French from Milan, which was restored to its Sforza dukes by the peace treaty in 1513.

[18] In 1502, the members of the Aragonese Cortes gathered in Zaragoza, and Parliaments of the Kingdom of Valencia and the Principality of Catalonia in Barcelona, as members of the Crown of Aragon, swore an oath of loyalty to their daughter Joanna as heiress, but Alonso de Aragón, Archbishop of Saragossa, stated firmly that this oath was invalid and did not change the law of succession which could only be done by formal legislation by the Cortes with the King.

[19][20] So, when King Ferdinand died on 23 January 1516, his daughter Joanna inherited the Crown of Aragon, and his grandson Charles became Governor General (regent).

With his wife Isabella I the Catholic (whom he married 19 October 1469), King Ferdinand had seven children: With his second wife, Germaine of Foix (whom he married on 19 October 1505 in Blois, Kingdom of France), King Ferdinand had one son: He also left several illegitimate children, two of them were born before his marriage to Isabella: With Aldonça Ruiz d'Ivorra i Alemany, a Catalan noblewoman of Cervera, he had: With Joana Nicolaua: With Toda de Larrea: With Beatriz Pereira: With an unknown mother, possibly of noble descent: Monarch of the Crown of Castille (with Isabella I) The Arms quarter the arms of Castile and León with the arms of Aragon and Aragonese Sicily, the last combining the arms of Aragon with the black eagle of the Hohenstaufen of Sicily.