The history of Spain reaches back into antiquity and the era of the Roman Empire. After the demise of Rome the Iberian Peninsula fractured into many kingdoms. Even as late as the 15th century, the most important among all of the separate Christian kingdoms that made up the old Hispania were the Kingdom of Castile (occupying northern and central portions of the Iberian Peninsula), the Kingdom of Aragon (occupying northeastern portions of the peninsula), and the Kingdom of Portugal occupying the far western Iberian Peninsula.
The death of King Henrique IV of Castile in 1474 set off a struggle for power called the War of the Castilian Succession (1475–1479). Contenders for the throne of Castile were Henrique IV’s one-time heir Joanna la Beltraneja, supported by Portugal and France, and Henrique’s half-sister Isabella of Castile, supported by the Kingdom of Aragon and by the Castilian nobility. The setting of the succession was a step in unifying Aragon and Castile into the Kingdom of Spain.
Isabella, Queen of Castile
Isabella was born on April 22, 1451 in Madrigal de las Altas Torres, Ávila, to King Juan II of Castile and his second wife, Isabella of Portugal, daughter of João, Constable of Portugal, (of the Aviz dynasty) the youngest surviving son of King João I of Portugal, and his half-niece and wife, Isabella of Barcelos, the daughter of his half-brother Afonso of Barcelos, the Duke of Braganza, an illegitimate son of the king.
At the time of her birth, Isabella was second in line to the throne after her older half-brother the future King Henrique IV of Castile. Henrique was 26 at the birth of his half-sister Isabella and was married to Queen Blanche II of Navarre but the union was childless and later annulled due to Henrique’s impotence. Another younger brother Alfonso of Castile was born two years later on November 17, 1453, lowering her position to third in line. When her father died in 1454, her half-brother ascended to the throne as King Henrique IV of Castile. Isabella and her brother Alfonso were left in King Henrique’s care. Isabell, her mother, and Alfonso then moved to Arévalo.
Henrique IV made a number of attempts throughout his reign to arrange a politically advantageous marriage for his much younger sister. The first attempt was when the six-year-old Isabella was betrothed to Fernando of Aragon and Navarre, son of Juan II of Aragon and Navarre (a cadet branch of the House of Trastámara) and his second wife, Juana Enriquez de Córdoba, 5th Lady of Casarrubios del Monte the daughter of Fadrique Enríquez de Mendoza and Mariana Fernández de Córdoba y Ayala, 4th Lady of Casarrubios del Monte, she was a great-great granddaughter of Alfonso XI of Castile.
In March 1453, before the annulment between King Henrique IV of Castile from Queen Blanche II of Navarre was finalised, there is no record of negotiations for the new marriage between Henrique IV and Joan of Portugal, sister of the king Alfonso V of Portugal. The first marital approaches were made in December of that year, although the negotiations were long and the proposal wasn’t definitively agreed until February 1455. The wedding was celebrated in May 1455, but without an affidavit of official bull authorizing the wedding between them, they were first cousins (their mothers were sisters) and second cousins (their paternal grandmothers were half-sisters). On February 28, 1462, the queen gave birth to a daughter Joanna la Beltraneja, whose paternity came into question during the conflict for succession to the Castillian throne when Henrique IV died.
In 1468, at the age of only 14, Alfonso, the brother of Henrique IV and Isabella, died, most likely from the plague (although poison and slit throat have been suggested). His will left his crown and place in the succession to his sister, Isabella. Henrique IV agreed to exclude Joanna la Beltraneja from the succession, due to her questionable parentage, and to recognize Isabella as his official heir.
Fernando II, King of Aragon
Infante Fernando of Aragon married Infanta Isabella, on October 19, 1469 in Valladolid, Kingdom of Castile and Leon. Isabella also belonged to the royal House of Trastámara, and the two were cousins by descent from Juan I of Castile. They were married with a clear prenuptial agreement on sharing power, and under the joint motto “tanto monta, monta tanto”.
Isabella became Castile’s next monarch when King Henrique IV died in 1474. However, the succession was not settled. After the death of King Henrique IV, war broke out in Castile. Joanna la Beltraneja was supported by Portugal, while the eventual winner, Henrique’s half-sister Isabella I of Castile, had the support of Aragon. France initially supported Joanna, yet in 1476, after losing the Battle of Toro, France refused to help Joanna, further and in 1478 signed a peace treaty with Isabella.
Fernando II and Isabella I, King and Queen of Castile and Aragon
Upon Isabella’s succession to the throne of Castile, she ruled jointly with her husband, Fernando of Aragon who succeeded his father as King Fernando II of Aragon in 1479,
Their marriage united both crowns and set the stage for the creation of the Kingdom of Spain, at the dawn of the modern era. That union, however, was a union in title only, as each region retained its own political and judicial structure. Pursuant to an agreement signed by Isabella and Fernando on January 15, 1474, Isabella held more authority over the newly unified Spain than her husband, although their rule was shared. Together, Isabella of Castile and Ferdinand of Aragon were known as the “Catholic Monarchs” (Spanish: los Reyes Católicos), a title bestowed on them by Pope Alexander VI.