When Ferdinand of Aragon and Isabella of Castille married in 1469 they formed what would become known as Spain. Ruling together this ‘power couple’ turned Spain into a Superpower. They were both politically savvy enough to know that they needed to make alliances with other countries in order to keep the political stability they had established in Spain.
The politically arranged marriage between Ferdinand and Isabella was intended to unite the two kingdoms. When Henry IV of Castile died in 1474, Isabella had herself proclaimed queen in Segovia with Ferdinand at her side as king consort. They won a war of succession against Afonso V of Portugal in 1479 who supported Juana la Beltraneja´s succession rights. The same year in which Ferdinand acceded to the throne of Aragon.
- The reform of the administration in Castile by creating courts in Valladolid and Granada ( Chancilllerias and Audiencias). A rural police, the Holly Brotherhood was implemented to control rural áreas. Army was reformed and tercios were created to improve war strategies.
- They broke the power of the nobles and acquired all their lands.
- Religious unity: Isabella and Ferdinand banned all religions other than Roman Catholicism—a deed for which they earned the title Los Reyes Católicos (The Catholic Monarchs)—and obtained from the pope the right to appoint all high church dignitaries. In 1478 they established the Spanish Inquisition to enforce religious uniformity In 1492 the Inquisition was empowered to expel from the kingdom all Jews who refused to be baptized, a move to strengthen the Church and to gain its support for the crown. This move proved to be unwise as it deprived Spain of some of its most influential and cultured citizens.
- Territorial unity: After having united the Crowns of Castile and Aragon, in 1482 Ferdinand began directing military campaigns against the kingdom of Granada, the last foothold of the Muslims in Spain. The Muslims were finally defeated on Jan. 2, 1492, and those who would not convert to Catholicism were expelled from Spain. Later on in 1511, using war and diplomacy, Navarre was annexed to the Spanish Crown then the territorial unity was completed.
- The conquest of Granada left Ferdinand time to support the first voyage of Columbus across the Atlantic Ocean.
- Foreign policy was based on King Ferdinand´s decissions focussed on Africa, the Atlantic and Europe. Castile was oriented to the Atlantic after the discovery of America but also conquered Melilla, Oran , Algiers and Trípoli as well as the Canary Islands. On the other hand, Aragon mantained its fight with France to control the southern part of present France (Cerdanay and Rousillon) as well as the South of Italy where Aragon controlled the Kingdom of Naples.