At the time of Isabella’s birth in 1451, the Iberian Peninsula was divided into three separate kingdoms: Aragon, Castile and Portugal. The balance of power was maintained thanks to a complex interplay of wars, short-term political alliances and marriages between the three royal houses. All three kingdoms were engaged in internal struggles between the authority of the crown and the privileges of the great nobles. As trade increased, the growth of cities meant that far-reaching reforms and the establishment of centralised government, with a single centralised tax system, became a priority. That, in turn, put an end to the autonomy of the powerful aristocratic landowners.

Daughter of John II of Castile and his second wife, Isabella of Portugal, the young Isabella had a brother, Henry IV, who came to the throne of Castile when King John died in 1554. The ineffectual Henry had a daughter Joanna, known as “la Beltraneja” because she was commonly believed to be the child not of Henry but of his favourite, Beltrán de la Cueva. The question of the royal succession therefore remained unsettled; finally, in 1468, Isabella was designated Princess of Asturias and heir to the Castilian throne. Isabella was now faced with the difficult choice of a suitable husband in terms of the existing political ground rules, a choice which would have vital implications for the geo-political future of the Peninsula. Contrary to the wishes of her brother, Isabella chose the young Prince Ferdinand, King of Sicily and heir to the Crown of Aragon. Her decision met with the hostility of both the French and the Portuguese, who did not take kindly to the threat of a powerful alliance between Castile and Aragon.

When Henry IV died in 1474, despite opposition from the supporters of Joanna la Beltraneja, Isabella was proclaimed Queen of Castile. When Ferdinand came the throne of Aragon following the death of his father in 1479, the two kingdoms took a giant step towards a new “Spanish” political and military unity. Although each of the two kingdoms retained sovereignty under its own monarch, the royal couple governed in partnership, thus exerting a unifying force and reinforcing the image of centralised power. Isabella fostered administrative reform in Castile, beginning with the measures adopted by the Cortes, or Parliament, of Toledo in 1480; she instituted a permanent military force for the protection of citizens and their property (known as the Santa Hermandad, or Holy Brotherhood), she cut back the privileges of the nobles and introduced a unified legal system.

Religion played a key role in the politics of the two sovereigns. Even before Pope Alexander VI bestowed on them the official title of “the Catholic Monarchs” in 1496, they embodied the ideals of a political power that was devoted to furthering the interests of the Catholic faith. The legitimacy of their mission was grounded in their consecrated role in carrying out the will of God for Spanish Christians. The establishment of the Inquisition in 1478 was part of that divine mission; it was designed to replace the autonomy of the local bishoprics with a unified and tightly regulated court of law controlled by the State. The conquest in 1492 of Granada, the last Moorish kingdom in the Peninsula, the expulsion of the unconverted Jews and the unconverted Moslems, in 1492 and 1502, respectively, were the other elements of their constant policy of defence of the “true faith”. Also in 1492, Christopher Columbus’s discovery of the Americas, apart from the economic interests involved, created an image of the Catholic Monarchs committed to converting a whole new continent to Christianity.

Isabella’s political projects came perilously close to failure, however. The grief over the death of her only male heir, Prince John, in 1497, fuelled fears of a new war of succession. Moreover, her daughter Joanna, the wife of the Hapsburg, Philip the Fair of Burgundy, and mother of the future Charles V, was already showing signs of the mental illness which would cause her to go down in history as Joanna the Mad. Heart-broken, Isabella died in 1504, but her historic vision of the Iberian Peninsula was to survive to the present day.