Born in madrigal de las Torres, Avila in Spain on 22 April 1451, Isabella was the daughter of John II of Castile and his second wife, Isabella of Portugal. Three years after her birth, when her father died in 1454, her half brother became the King as Henry IV and apprehending possible troubles, Isabella’s mother quietly moved to Arevalo, with her daughter and her younger son, Alfonso. However, before the birth of her daughter Joanna, they were summoned to the court in Segovia to come under the direct supervision of the King. Isabella got her basic education there, which included reading, writing, mathematics, art, music, chess, embroidery, and religious instructions.
However, the noble at the court were anxious to grab power and they confronted the King, demanding that his half brother Alfonso should be named his successor. Finally, they clashed with Henry's forces at the Second Battle of Olmedo in 1467. Though the battle was a draw, King Henry agreed to recognize Alfonso as his heir, provided he would marry his daughter, Princess Joanna la Beltraneja. However, as Alfonso suddenly died in July 1468, likely of the plague, the rebellious nobles turned to Isabella and requested her to take the place of her younger brother as their leader. But, Isabella was not interested to play that designated role and preferred a negotiated solution of the issue. She met Henry at Toros de Guisando and it was agreed that, the war would stop, instead of Henry’s daughter Joanna, Isabella would be named as his heir-presumptive, Isabella would not marry without Henry’s consent, but Henry would not be able to force her to marry against her will.
Since Isabella was the heiress of Castile, the question of her future marriage was an important diplomatic issue. There was talk of a marriage to Edward IV of England or to his brother Richard, but that alliance was never considered seriously. When a proposal came from Alfonso V of Portugal in 1468, Henry wanted to make it a reality, since he quickly realized that, in the long run it would be beneficial for her daughter Joanna. In case of Isabella’s marriage to Alfonso, Joanna would marry Alfonso's son John II and thus, after the death of the old king, John and Joanna would inherit Portugal and Castile. But, Isabella bluntly refused the proposal. But Henry did not stop despite his failed attempt and desperately tried to make arrangements to marry Isabella with Louis XI’s brother Charles, since it would cement the friendship of Castile and France and also remove Isabella from Castilian affairs. However, once again Isabella refused the proposal. In the meantime, John II of Aragon negotiated in secret with Isabella a wedding to his son Ferdinand, to which Isabella agreed and secretly promised to marry her cousin, Ferdinand of Aragon. To avoid possible opposition, she eloped from the court of Henry with the excuse of visiting her brother’s tomb in Avila and without Henry’s approval married Ferdinand on 19th October 1469, in Palacio de los Vivero, in Valladolid.
However, on receipt of the news of King Henry IV’s death on 12 December 1474, Isabella immediately took refuge in the Alcazar of Segovia castle. There she received the support of Andres Cabrera and Segovia's council and on the next day, was crowned as Queen of Castile and León. The opposing faction, supporters of Joanna, included the archbishop of Toledo, a former supporter of Isabella, the powerful young marques de Villena and the master of Calatrava. They were also supported by Afonso V of Portugal, who proceeded to invade Castile and married the young Joanna, the daughter of the late King. The ensuing long and bloody war lasted till 1 March 1476, when in the Battle of Toro, the troops of King Alfonso V were beaten. Consequently, the supporters of Joanna la Beltraneja were disbanded and the Portuguese army, without allies, left Castile for their country. Upon the death of John II of Aragon in the same year, the kingdoms of Castile and Aragon came together in the persons of their rulers.
In the month of August, in the same year, Isabella proved her abilities again as a powerful ruler. A rebellion broke out in Segovia and against the advice of her advisors, she rode out to suppress it. But, instead of taking extreme measures, she successfully negotiated with the rebels and amicably settled the issue.
As Ferdinand in his first will made Isabella his heir in Aragon, Spain emerged as a united country. But it was decided that the two sovereigns, Aragon and Castile, would be governed according to their own institutions and the ultimate aim of the union would be to end the long process of Reconquista, the untiring efforts of the Christian kings of the Spanish kingdoms to reclaim their country from the Moors, which continued for eight centuries. The end of the proceeds means, the taking over the kingdom of Granada, the last Muslim stronghold in Spain. The Emirate of Granada, protected by natural barriers and fortified towns, was held by the Muslim Nasrid Dynasty since the mid 13th Century. Isabella and her husband reached Medina del Campo on 1 February 1482, which is generally considered as the beginning of the war for Granada. But, though the Muslim Leadership in Granada was divided into different groups and could never present a united front, it took long ten years to conquer Granada. In an attempt to start the final assault, Isabella and Ferdinand set up a forward headquarters in Santa Fe in 1491 and stayed there, till Granada fell on January 2, 1492.
Meanwhile, the Castilian and Portuguese fleets were fighting over the dominance in the Atlantic Ocean and for the wealth of Guinea, in terms of gold and slaves. The long war ended with a Castilian victory on land and a Portuguese victory in the sea. As per treaties signed at Alcacovas on the 4th of September 1479, the Portuguese accepted Isabella on the throne of Castile in exchange of their favourable share of the Atlantic territories disputed with Castile. However, the absolute Portuguese right of navigation and commerce in all of the Atlantic Ocean south of the Canary Islands, actually blocked Spain out of the Atlantic and deprived of the gold of Guinea. Christopher Columbus saved Castile from this difficult situation, as his New World discovery led to a new and much more balanced sharing of the Atlantic at Tordesillas in 1494.
While Isabella was in Santa Fe, Christopher Columbus visited her, requesting her support for his expeditionary voyage to discover a new route to reach the Indies, which would finally result in the European settlement of America. The crown agreed to pay a certain sum of money and it was obvious that, in return, it would be reciprocated with the credit for approving the proposal of the epoch-making voyage. Columbus departed on 3 August 1492, arrived in San Salvador Island on 12 October and named it after Jesus the Savior. He returned the next year and was given a hero’s welcome, while he presented his findings to the monarchs, along with the slaves, in the form of the imprisoned natives and gold. The new world, thus explored as the result of the decision of royal approval, was annexed to the crown of Castile with the papal confirmation. Isabella, however, differed with Columbus about the idea of 'slaves', she and her councillors were ready to recognize the rights of the Indians and accordingly ordered some of those Columbus had brought back as slaves to be released.
The reign of Isabella I, was marked by the Tribunal of the Holy Office of the Inquisition, otherwise known as the Spanish Inquisition, which was established in 1478 by the Catholic Monarchs, Ferdinand II and Isabella I of Castile. It was intended to maintain Catholic orthodoxy in their kingdoms. Personally, Isabella was against taking any harsh measure against the Jews on economic ground. But, Tomás de Torquemada, the first Grand Inquisitor in Spain's movement to homogenize religious practices, convinced Ferdinand to promulgate the Alhambra decree for the expulsion of the Jews on 31st March 1492. Three month’s time, till the end of July, was allotted to the Jews to leave the country, without taking any gold, silver, money, arms, or horses with them. It was claimed that during the scheduled period as many as 200,000 Jews left Spain. But, recent studies have shown that, out of a total population of 80,000 Jews, a maximum of 40,000 left the country and the rest were converted. Hundreds of those that remained in the country came under the watchful eye of the Spanish Inquisition, subject to suspicions of the secret practice of Judaism. Yet, they took the risks and continued to practice Judaism in secret and were known as Marranos.
During the reign of Isabella I and Ferdinand, the Royal Council was traditionally the main advisory body to the rulers of Castile. It was also the supreme judicial tribunal of the kingdom. While the Council, under the monarch, had full power to resolve all the legal and the political disputes, it was responsible for supervising all the senior administrative officials. Unlike the past, Isabella began to rely more on the professional administrators for the smooth running of the government. These men were mostly of the bourgeoisie or lesser nobility. It was rearranged and was officially settled that, one bishop, three caballeros (knights) and eight or nine lawyers would serve on the council at a time. While the nobles were no longer directly involved in the matters of state, they were welcome to attend the meetings. Isabella contemplated that, if the nobles were forced to choose whether they would participate in the function of the government, the non-participants would be automatically marked as not dedicated to the state and its cause. The Council of State was also reformed and presided over by the King and Queen. Throughout her long reign, Isabella also strove to strengthen the royal authority at the expense of the Cortes or the Spanish parliament and the towns.
During the late medieval period, the term hermandad was 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 the malefactors. But, usually the monarch had the tendency to suppress these brotherhoods. To fix this problem, during 1476, a general Hermandad was established for Castile, Leon and Asturias. This paid police force was to be made up of locals who were to regulate the crime occurring in the kingdom. The reign of Henry IV had left the kingdom of Castile in great debt. To make money, Henry had sold off royal estates at prices well below their value. It was decided that, an enquiry would be held by the Cardinal of Spain, regarding the tenure of estates and rents acquired during the reign of Henry IV. Those that had not been granted as a reward for services were to be restored without compensation, while those that had been sold at a price far below their real value were to be bought back at the same sum. While many of the nobility were forced to pay large sums of money for their estates, the royal treasury became ever richer. Isabella also stipulated that there would be no revocation of gifts made to churches, hospitals, or the poor.During Henry's reign, the number of mints regularly producing money had increased from just five to 150. Isabella established a monopoly over the royal mints and fixed a legal standard to which the coinage must approximate. With the closure of the numerous 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 finance.
With her strong and stocky build, very fair complexion, blue eyes, chestnut hair, her jewels and magnificent dresses, Isabella must have made a striking figure. She was intensely pious and orthodox in her beliefs and was granted with Ferdinand the title of the ‘Catholic Kings’ by Pope Alexander VI. But she was not happy with the Pope. She thought the pope was making bad appointments to Spanish benefices or in any way encroaching on the customary rights of the crown over the Spanish churches. Isabella and Ferdinand commenced a process of spiritual unification, trying to bring the country under one faith, Roman Catholicism. As a part of this process, the Inquisition became institutionalised. There was a Muslim uprising in 1499 and after that when the Treaty of Granada was broken in 1502, the Muslims were ordered to either become Christians or to leave. Isabella's confessor, Cisneros was named Archbishop of Toledo.
Like religion, Isabella was also very much interested in education. She acquired proficiency in Latin, after she reached the age of thirty. At court, she encouraged notable scholars and many of the outstanding literary works of her reign were dedicated to her. She was also the patron of Spanish and Flemish artists.
The last decade of her reign was sad and marked by family disasters. Her only son and heir, Prince John of Asturias died untimely in 1497 and her daughter Isabella, Queen of Portugal, died in the next year in childbirth. As if that was not enough, she also lost her grandchild Miguel in 1500. After her official withdrawal from the governmental affairs on 14th September 1504, Isabella died in the same year on 26 November at the Medina del Campo Royal Palace. It is said that her health was steadily in decline since the death of her son. She is entombed in Granada in the Capilla Real, built by Holy Roman Emperor Charles V, her grandson, the son of her daughter Joan.