Isabella I (Spanish: Isabel I; 22 April 1451 – 26 November 1504),[2] also called Isabella the Catholic (Spanish: Isabel la Católica), was Queen of Castile and León from 1474 until her death in 1504. She was also Queen of Aragon from 1479 until her death as the wife of King Ferdinand II. Reigning together over a dynastically unified Spain, Isabella and Ferdinand are known as the Catholic Monarchs.[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. Isabella's marriage to Ferdinand in 1469 created the basis of the de facto unification of Spain. Her reforms and those she made with her husband had an influence that extended well beyond the borders of their united kingdoms.[4]
Isabella I of Castile and Ferdinand II of Aragon are known for being the first monarchs to be referred to as the "Queen of Spain" and "King of Spain", respectively. Their actions included completion of the Reconquista, the Alhambra Decree which ordered the mass expulsion of Jews from Spain, initiating the Spanish Inquisition, financing Christopher Columbus's 1492 voyage to the New World, and establishing the Spanish empire, making Spain a major power in Europe and the world and ultimately ushering in the Spanish Golden Age.[5] Together with her husband, Isabella was granted the title of "Catholic Monarch" by the Spanish Pope Alexander VI, and was recognized in 1974 as a Servant of God by the Catholic Church.
Isabella was born in Madrigal de las Altas Torres to King John II of Castile and his second wife, Isabella of Portugal, on 22 April 1451.[6] At the time of Isabella's birth, she was second in line to the throne after her older half-brother Henry.[5] Henry was 26 at that time and married, but childless. Isabella's younger brother Alfonso was born two years later on 17 November 1453, demoting her position to third in line.[7] When her father died in 1454, her half-brother ascended to the throne as King Henry IV. Isabella and her brother Alfonso were left in King Henry's care.[8] Isabella, her mother, and Alfonso then moved to Arévalo.[5][9]
These were times of turmoil for Isabella. The living conditions at their castle in Arévalo were poor, and they suffered from a shortage of money. Although her father arranged in his will for his children to be financially well taken care of, King Henry did not comply with their father's wishes, either from a desire to keep his half-siblings restricted or from ineptitude.[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.[9]
When the king's wife, Joan of Portugal, was about to give birth to their daughter Joanna, Isabella and her brother Alfonso were summoned to court in Segovia to come under the direct supervision of the king and to finish their education.[5] Alfonso was placed in the care of a tutor while Isabella became part of the queen's household.[10]

Isabella in the
Rimado de la Conquista de Granada, from 1482, by Pedro Marcuello
Some of Isabella's living conditions improved in Segovia. She always had food and clothing and lived in a castle that was adorned with gold and silver. Isabella's basic education consisted of reading, spelling, writing, grammar, history, arithmetic, art, chess, dancing, embroidery, music, and religious instruction. She and her ladies-in-waiting entertained themselves with art, embroidery, and music. She lived a relaxed lifestyle, but she rarely left Segovia since King Henry forbade this. Her half-brother was keeping her from the political turmoil going on in the kingdom, though Isabella had full knowledge of what was going on and of her role in the feuds.[11][better source needed]
After a rumor spread that Joanna was not actually the daughter of King Henry but rather of a royal favorite, Beltrán de la Cueva, noblemen confronted King Henry and demanded that the king's younger half-brother Alfonso be named his successor. They even went so far as to ask Alfonso to seize the throne. The nobles, now in control of Alfonso and claiming that he was the true heir, clashed with King Henry's forces at the Second Battle of Olmedo in 1467. The battle was a draw. King Henry agreed to recognize Alfonso as his heir presumptive, provided that he would marry his daughter, Princess Joanna.[5][12] Soon after he was named Prince of Asturias, he died at the age of fourteen in July 1468. The nobles who had supported him suspected poisoning. As she had been named in her brother's will as his successor, the nobles asked Isabella to take his place as champion of the rebellion.[5] However, support for the rebels had begun to wane, and Isabella preferred a negotiated settlement to continuing the war.[13] She met with her elder half-brother Henry at Toros de Guisando and they reached a compromise: the war would stop, King Henry would name Isabella his heir presumptive instead of his daughter Joanna, and Isabella would not marry without her half-brother's consent, but he would not be able to force her to marry against her will.[5][14] Isabella's side came out with most of what the nobles desired, though they did not go so far as to officially depose King Henry; they were not powerful enough to do so, and Isabella did not want to jeopardize the principle of fair inherited succession, since it was upon this idea that she had based her argument for legitimacy as heir-presumptive.
The question of Isabella's marriage was not a new one. 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.[15] This arrangement, however, did not last long.

The wedding portrait of Ferdinand and Isabella,
c. 1469
Ferdinand's uncle Alfonso V of Aragon died in 1458. All of Alfonso's Spanish territories, as well as the islands of Sicily and Sardinia, were left to his brother John II. John now had a stronger position than ever before and no longer needed the security of Henry's friendship. Henry was now in need of a new alliance. He saw the chance for this much-needed new friendship in Charles of Viana, John's elder son.[16] Charles was constantly at odds with his father, and because of this, he secretly entered into an alliance with Henry IV of Castile. A major part of the alliance was that a marriage was to be arranged between Charles and Isabella. When John II learned of this arranged marriage, he was outraged. Isabella had been intended for his favorite younger son, Ferdinand, and in his eyes, this alliance was still valid. John II had his son Charles thrown in prison on charges of plotting against his father's life. Charles died in 1461.[17]
In 1465, an attempt was made to marry Isabella to Afonso V of Portugal, Henry's brother-in-law.[5] Through the medium of the queen and Count of Ledesma, a Portuguese alliance was made.[18] Isabella, however, was wary of the marriage and refused to consent.[19]
A civil war broke out in Castile over King Henry's inability to act as sovereign. Henry now needed a quick way to please the rebels of the kingdom. As part of an agreement to restore peace, Isabella was then to be betrothed to Pedro Girón Acuña Pacheco, Master of the Order of Calatrava and brother to the king's favorite, Juan Pacheco.[18] In return, Don Pedro would pay into the royal treasury an enormous sum of money. Seeing no alternative, Henry agreed to the marriage. Isabella was aghast and prayed to God that the marriage would not come to pass. Her prayers were answered when Don Pedro suddenly fell ill and died while on his way to meet his fiancée.[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.[5][14] It seemed that the years of failed attempts at political marriages were finally over. There was talk of a marriage to Edward IV of England or to one of his brothers, probably Richard, Duke of Gloucester,[21] but this alliance was never seriously considered.[14] Once again in 1468, a marriage proposal arrived from Afonso V of Portugal. Going against his promises made in September 1468, Henry tried to make the marriage a reality. If Isabella married Afonso, Henry's daughter Joanna would marry Afonso's son John II and thus, after the death of the old king, John and Joanna could inherit Portugal and Castile.[22] Isabella refused and made a secret promise to marry her cousin and very first betrothed, Ferdinand of Aragon.[5]