The Catholic Monarchs:

In the first half of the 15th century, the Iberian peninsula was divided into 5 different large territories:
.- The Crown of Castile
.- The Crown of Aragon
.- The Kingdom of Navarra
.- The Kingdom of Portugal
.- The Islamic Kingdom of Granada.

In 1469 Ferdinand II of Aragon and Isabella I of Castile got married, thus promoting the future union of both kingdoms. They took several important measures to reinforce their authority:
.- They created the Holy Brotherhood (a kind of police)
.- They created a professional army
.- They also created courts of justice called "Chancillerías".
.- They created a number of royal councils to advise the monarchs.

They also expanded the territories by conquering the Kingdom of Granada (1492), the Canary Islands (1496), Melilla (1497) and Oran (1509) and Navarra (1512). Besides, they financed Columbus voyage, leading to the acquisition of territories in America (1492), and acquired the Kingdom of Naples (1504).

The Catholic Monarchs also promoted the religious unity by creating a church tribunal, the Inquisition (1478), then expelling the Jews (1492) and expelling or converting the Muslims (1502).