[3] After a struggle to claim the throne, Isabella reorganized the governmental system, brought the crime rate down, and unburdened the kingdom of the debt which her half-brother King Henry IV had left behind.

[8] Even though her living conditions were difficult, Isabella was instructed in lessons of practical piety and in a deep reverence for religion under the supervision of her mother.

Isabella's basic education consisted of reading, spelling, writing, grammar, history, arithmetic, art, chess, dancing, embroidery, music, and religious instruction.

She had, at the age of six, a betrothal to Ferdinand, the younger son of John II of Navarre (whose family was a cadet branch of the House of Trastámara).

At that time, the two kings, Henry and John, were eager to show their mutual love and confidence and they believed that this alliance would make their eternal friendship obvious to the world.

[18][20] When Henry had recognized Isabella as his heir-presumptive on 19 September 1468, he had also promised that his half-sister should not be compelled to marry against her will, while she in return had agreed to obtain his consent.

Diego Pacheco, the Marquis of Villena, and his followers maintained that Joanna la Beltraneja, Henry's daughter, was the rightful queen.

But despite its uncertain[43][44] outcome, the Battle of Toro represented a great political victory[45][46][47][48] for the Catholic Monarchs, assuring them the throne since the supporters of Joanna la Beltraneja disbanded and the Portuguese army, without allies, left Castile.

[55] The four separate peace treaties signed at Alcáçovas (4 September 1479) reflected that result: Portugal gave up the throne of Castile in favor of Isabella in exchange for a very favorable share of the Atlantic territories disputed with Castile (they all went to Portugal with the exception of the Canary Islands:[56][57] Guinea with its mines of gold, Cape Verde, Madeira, Azores, and the right of conquest over the Kingdom of Fez[58][59]) plus a large war compensation: 106.676 dobles of gold.

[61] And the Catholic Monarchs – who had proclaimed themselves rulers of Portugal and donated lands to noblemen inside this country[62] – had to give up the Portuguese crown.

[64] Christopher Columbus freed Castile from this difficult situation, because his New World discovery led to a new and much more balanced sharing of the Atlantic at Tordesillas in 1494.

On 13 December 1474, in Segovia's main square, Isabella pledged to uphold the Church's commandments, protect the integrity of Castile, and respect the rights of the nobility and towns.

[67] Isabella's first major reform came during the cortes of Madrigal in 1476 in the form of a police force, La Santa Hermandad (the Holy Brotherhood).

[68] During the late medieval period, the expression hermandad had been used to describe groups of men who came together of their own accord to regulate law and order by patrolling the roads and countryside and punishing malefactors.

During the first year of her reign, Isabella established a monopoly over the royal mints and fixed a legal standard to which the coinage had to approximate[citation needed].

By shutting down many of the mints and taking royal control over the production of money, Isabella restored the confidence of the public in the Crown's ability to handle the kingdom's finances.

The first body was made up of household officials, mainly people of the nobility, who carried out governmental and political functions for which they received special payment.

This department of public affairs dealt mainly with foreign negotiations, hearing embassies, and transacting business with the Court of Rome.

Isabella and her husband moved in the direction of a non-parliamentary government and the Cortes became an almost passive advisory body, giving automatic assent to legislation which had been drafted by the royal administration.

[84] After the reforms of the Cortes of Toledo, the queen ordered a noted jurist, Alfonso Diaz de Montalvo, to undertake the task of clearing away legal rubbish and compiling what remained into a comprehensive code.

Isabella and her husband had created an empire and in later years were consumed with administration and politics; they were concerned with the succession and worked to link the Spanish crown to the other rulers in Europe.

[109] Luisa de Medrano's intellectual abilities and solid formation caught the attention of the Queen and enabled her to teach Latin at the University of Salamanca.

[110] Under the protection of Queen Isabel I, Luisa de Medrano learned history, culture and humanist philosophy alongside children of the royal family.

[111] Isabella officially withdrew from governmental affairs on 14 September 1504 and she died that same year on 26 November at the Medina del Campo Royal Palace.

[112] She is entombed in Granada in the Capilla Real (built by her grandson, Charles V, Holy Roman Emperor), alongside her husband Ferdinand, her daughter Joanna, and other relatives.

[citation needed] However, the statue of her in Granada Cathedral, by Burgundian sculptor Philippe de Vigarny (born in Langres, in what is now France), also shows her as a dark-haired brunette.

Her daughters Joanna and Catherine were thought to resemble her the most in looks - both are similarly described in contemporary sources as having auburn hair, but surviving paintings often show them as brunettes due to the same pigmentation problem.

Some authors have claimed that Isabella's reputation for sanctity derives in large measure from an image carefully shaped and disseminated by the queen herself.

[128] In April 2020, Cardinal Antonio Cañizares Llovera confirmed that Pope Francis had requested that the Spanish bishops reopen Isabella's cause for canonization.

As co-monarchs, Isabella and Ferdinand used the motto "Tanto Monta" ("They amount to the same", or "Equal opposites in balance"), which refers to their prenuptial agreement.