Isabelle I, girl of Jean II and his second Isabelle wife of Portugal, was born in Madrigal from mow Altas Torres, on on April 22nd, 1451. Nothing predisposed it to go up on the throne, since of its first marriage with Marie d' Aragon the king had had a son, Henri, and another of the second, the Alphonse infante. But, become king, Henri IV (1454-1474), whose manners are very disputed, does not manage to leave a heir to the crown: the Jeanne queen put well at the world, in 1462, a girl, but paternity is allotted to a gentleman named Beltrán of Cueva, from where the nickname of “Beltraneja” which was going to be given the princess. The Alphonse infante is thus designated as successor, but he dies in 1468: Isabelle thus proclaims heiress against Beltraneja, held for bastard. Although the partisans of Isabelle are numerous, the aristocracy Castilian, very powerful, is divided on the question of the succession, because Henri IV recognized his claimed daughter. Its marriage with the heir to the crown of Aragon, in 1469, was going to make it possible to Isabelle to impose itself like queen on the death of her brother, in 1474, and to carry it in Toro on the allies of his/her niece, among whom the king of Portugal (1476) was.

Isabelle I on the throne of Castille, the kingdom then knows a demographic dynamism without precedent, sufficiently marked to involve many clearings and the setting in new ground culture. The breeding of the sheep becomes one of the independent sources of incomes of Castille. It is controlled by Mesta (powerful association of stockbreeders, which organizes transhumance through the Peninsula). The essence of the wool production is exported towards Flandres. Castille also exports iron ore but, on the other hand, only few industries count.

Isabelle, anxious to restore interior peace after the disorders of the civil war, set up in 1476 a police force, Santa Hermandad, which results from the transformation of the urban militia of the Middle Ages into a force centralized, charged continuing the gangsters, with supervising the campaigns and the ways of the kingdom; the delinquents are judged by the alcaldes of Santa Hermandad, which apply extremely severe sorrows to them. The dissolution of this force will be marked only in 1498, after the re-establishment of the order. Being based on the clergy and the middle-classes, Isabelle restores the wheels of the monarchical government: The royal Council, corregidores in the cities, audiencia for justice, and subject the military orders to the royal power

In 1478, the queen obtains from the pope Sixte IV the creation of a new court inquisitorial, intended to flush out and continue the heretics, the new converts and, gradually, all the opponents with the royal power. In 1483 the Council of Suprema (Consejo supremo of Santa Inquisición) is created, which second the Grand inquisitor in the treatment of the questions concerned with the Enquiry at the governmental level.

From 1480, Isabelle abolishes most privileges of the nobility - Castilian, Andalusian or Galician - obtained under the reign of Henri IV, to gradually put it at the step. In the same spirit, it places, in 1487, in charge of the order of Calatrava, one of the very powerful orders of knighthood of the kingdom, her husband, the king Ferdinand II of Aragon. The queen reinforces the powers of the royal Council and proceeds to a reform of the taxation, which touches the Church itself, before increasing the taxes. At the same time, the sovereign one supports the disciplinary reformation of the convents and the secular clergy. The cities, which initially helped it to fight the power peerage-book, in their turn are placed under the control of monarchy.

From 1481, Isabelle launches many offensives against the kingdom of Grenade, which politically corresponds to multiple projects: to complete the Christian Reconquest, to annex new territories and to channel quarrelsome moods of the nobility Castilian. Lengthily negotiated by Kings Catholiques, the rendering of Grenade is obtained, after a long seat, on on January 6th, 1492. The kingdom of Grenade becomes a province of the kingdom of Castille, controlled by a viceroy whose main mission is the conversion of the Moors to Christianity.

But, vis-a-vis the reserves of the population, violence becomes the mode of expression of the power and will cause a general rising, quickly crushed. The Christian victory is accompanied by the confiscation of the grounds, which are then redistributed with the winners. The Moors, driven out cities where they exerted artisanal trades, settle in the countryside. The practice of their religion and the Koranic right is tolerated, but, on the other hand, they are held to work the ground. Kings Catholiques support the migration of the peasants of Castille towards the areas devastated by the wars, and very quickly the latter enter in conflict with the country Moors, the mudéjares. In addition, in order to maintain the industrial activities and commercial cities, in particular in Grenade, the Christian families are encouraged to come to settle there, in spite of the opposition of the Moors: a pattern of the settlement by religion is installation by districts. The Jews are obliged to convert, under penalty of expulsion, since 1492. Ten years later, a similar measure will be taken against the mudéjares.

Shortly after the fall of Grenade, and on the pressing councils of certain members of his entourage, in particular of the treasurer of king Ferdinand, Luís de Santangel, Isabelle agrees to accept responsibility for the projects of a sailor of Genoese origin, Christophe Colomb, who proposes to rejoin the coasts of the Indies by the west, while crossing the Atlantic Ocean. It is initially in Portugal that Colomb offered its services, but the kingdom, more interested by the road of the Indian Ocean to reach the Indies, declined the offer; also the navigator it turned to Castille, for a long time interested by the development of navigation and the colonial expansion in the archipelagoes close to the African coasts, such that of the Canaries, as at the same time the Portuguese in Madeira did it or in the Azores.

The Castilians, reticent initially, finally agree to finance forwarding (the payments are made as alms with the title of the crusade, and the participation of ship-owners and tradesmen, in particular Pinzón, are important). The three caravels of Colomb, Niña, Boozed it and Santa María, leave the port of Palos, in Andalusia, on on August 3rd, 1492, then the Canaries on on September 6th, to reach finally, on on October 12th, an unknown island baptized at once San Salvador, and later Santo Domingo (Santo Domingo). Cuba is reached on on December 6th, but Colomb believes being arrived at Cipango (current Japan). On March 15th, 1493, the Genoese one is of return to Palos, where, preceded by the advertisement by its discovery, it is accommodated triumphantly.

To the death of Isabelle (1504), Castille returns to his/her Jeanne daughter the Insane one who is married in Philippe the Beautiful, son of the Maximilien emperor of Austria. Jeanne is unable to reign, and Philippe dies in 1506. Their son, the future Charles Quint, is still a child: Ferdinand d' Aragon then controls the two kingdoms until his death in 1516. At this date, Charles Quint inherits Spain, which, by the will of Kings Catholiques, became a State, a nation, an empire.