When King Ferdinand and Queen Isabella completed the conquest of the Kingdom of Granada from Muslim rule in 1492, they implemented policies to maintain control of the territory. To do so, the monarchy implemented a system of encomienda. This iteration of the encomienda system was land based, with tributary and land rights given to different noble families. This eventually led to a large land based aristocracy, a separate ruling class that the crown later tried to eliminate in its overseas colonies. By implementing this method of political organization, the crown was able to implement new forms of private property without completely replacing already existing systems, such as the communal use of resources. After the military and political conquest, there was an emphasis on religious conquest as well, leading to the creation of the Spanish Inquisition. Although the Inquisition was technically a part of the Catholic church, the Ferdinand and Isabella formed a separate Spanish Inquisition, which led to mass expulsion of Muslims and Jews from the peninsula. This religious court system was later adopted and transported to the Americas, though they took a less effective role there due to limited jurisdiction and large territories.
With the Christian reconquest completed in the Iberian peninsula, Spain began trying to take territory in Muslim North Africa. It had conquered Melilla in 1497, and further expansionism policy in North Africa was developed during the regency of Ferdinand the Catholic in Castile, stimulated by the Cardinal Cisneros. Several towns and outposts in the North African coast were conquered and occupied by Castile: Mazalquivir (1505), Peñón de Vélez de la Gomera (1508), Oran (1509), Algiers (1510), Bougie and Tripoli (1510). On the Atlantic coast, Spain took possession of the outpost of Santa Cruz de la Mar Pequeña (1476) with support from the Canary Islands, and it was retained until 1525 with the consent of the treaty of Cintra (1509).
The Catholic Monarchs had developed a strategy of marriages for their children in order to isolate their long-time enemy: France. The Spanish princesses married the heirs of Portugal, England and the House of Habsburg. Following the same strategy, the Catholic Monarchs decided to support the Aragonese house of Naples against Charles VIII of France in the Italian Wars beginning in 1494. As King of Aragon, Ferdinand had been involved in the struggle against France and Venice for control of Italy; these conflicts became the center of Ferdinand's foreign policy as king. In these battles, which established the supremacy of the Spanish Tercios in European battlefields, the forces of the kings of Spain acquired a reputation for invincibility that would last until the mid-17th century.
After the death of Queen Isabella in 1504, and her exclusion of Ferdinand from a further role in Castile, Ferdinand married Germaine de Foix in 1505, cementing an alliance with France. Had that couple had a surviving heir, likely the Crown of Aragon would have been split from Castile, which was inherited by Charles, Ferdinand and Isabella's grandson. Ferdinand adopted a more aggressive policy toward Italy, attempting to enlarge Spain's sphere of influence there. Ferdinand's first deployment of Spanish forces came in the War of the League of Cambrai against Venice, where the Spanish soldiers distinguished themselves on the field alongside their French allies at the Battle of Agnadello (1509). Only a year later, Ferdinand became part of the Holy League against France, seeing a chance at taking both Milan—to which he held a dynastic claim—and Navarre. This war was less of a success than the war against Venice, and in 1516, France agreed to a truce that left Milan in its control and recognized Spanish control of Upper Navarre, which had effectively been a Spanish protectorate following a series of treaties in 1488, 1491, 1493, and 1495.
Portugal obtained several Papal bulls that acknowledged Portuguese control over the discovered territories, but Castile also obtained from the Pope the safeguard of its rights to the Canary Islands with the bulls Romani Pontifex dated 6 November 1436 and Dominatur Dominus dated 30 April 1437. The conquest of the Canary Islands, inhabited by Guanche people, began in 1402 during the reign of Henry III of Castile, by Norman nobleman Jean de Béthencourt under a feudal agreement with the crown. The conquest was completed with the campaigns of the armies of the Crown of Castile between 1478 and 1496, when the islands of Gran Canaria (1478–1483), La Palma (1492–1493), and Tenerife (1494–1496) were subjugated.
The Portuguese tried in vain to keep secret their discovery of the Gold Coast (1471) in the Gulf of Guinea, but the news quickly caused a huge gold rush. Chronicler Pulgar wrote that the fame of the treasures of Guinea "spread around the ports of Andalusia in such way that everybody tried to go there". Worthless trinkets, Moorish textiles, and above all, shells from the Canary and Cape Verde islands were exchanged for gold, slaves, ivory and Guinea pepper.
The War of the Castilian Succession (1475–79) provided the Catholic Monarchs with the opportunity not only to attack the main source of the Portuguese power, but also to take possession of this lucrative commerce. The Crown officially organized this trade with Guinea: every caravel had to secure a government license and to pay a tax on one-fifth of their profits (a receiver of the customs of Guinea was established in Seville in 1475—the ancestor of the future and famous Casa de Contratación).
Castilian fleets fought in the Atlantic Ocean, temporarily occupying the Cape Verde islands (1476), conquering the city of Ceuta in the Tingitan Peninsula in 1476 (but retaken by the Portuguese),[c][d] and even attacked the Azores islands, being defeated at Praia.[e][f] The turning point of the war came in 1478, however, when a Castilian fleet sent by King Ferdinand to conquer Gran Canaria lost men and ships to the Portuguese who expelled the attack, and a large Castilian armada—full of gold—was entirely captured in the decisive battle of Guinea.[g]
The Treaty of Alcáçovas (4 September 1479), while assuring the Castilian throne to the Catholic Monarchs, reflected the Castilian naval and colonial defeat: "War with Castile broke out waged savagely in the Gulf [of Guinea] until the Castilian fleet of thirty-five sail was defeated there in 1478. As a result of this naval victory, at the Treaty of Alcáçovas in 1479 Castile, while retaining her rights in the Canaries, recognized the Portuguese monopoly of fishing and navigation along the whole west African coast and Portugal's rights over the Madeira, Azores and Cape Verde islands [plus the right to conquer the Kingdom of Fez ]." The treaty delimited the spheres of influence of the two countries, establishing the principle of the Mare clausum. It was confirmed in 1481 by the Pope Sixtus IV, in the papal bull Æterni regis (dated on 21 June 1481).
However, this experience would prove to be profitable for future Spanish overseas expansion, because as the Spaniards were excluded from the lands discovered or to be discovered from the Canaries southward—and consequently from the road to India around Africa—they sponsored the voyage of Columbus towards the west (1492) in search of Asia to trade in its spices, encountering the Americas instead. Thus, the limitations imposed by the Alcáçovas treaty were overcome and a new and more balanced division of the world would be reached in the Treaty of Tordesillas between both emerging maritime powers.