The Tudor connection: Isabella I of Castile and Ferdinand II of Aragon’s daughter was Katherine of Aragon, the wife of Prince Arthur of England, and later the wife of Henry VIII. Mary I was Isabella and Ferdinand’s grand-daughter. Their English line stopped with Mary I.
Spain was United
Isabella I of Castile and Ferdinand II of Aragon’s marriage technically did lead to the unification of Spain, although it wasn’t under their leadership, or even that of their successor, their daughter Juana (known as The Mad). Unification came under the rule of their grandson, the Holy Roman Emperor, Charles V. The unity would have occurred earlier had Isabella and Ferdinand’s only son, Juan, had survived childhood. Juan did get married, but his wife, Margaret of Austria, didn’t have a child by him, and a baby king would have been no good anyway.
The conquest of Granada in 1492 brought the last Spanish outpost under monarchical control. It had previously been under the control of the Moors. It was annexed into Castile, the closest Spanish kingdom. It was seen as a triumph for Christianity. This did lead to severe problems with the Islamic population, however. Nevertheless, Granada made Spain a more united country, because all of it was under the control of the same monarchy and government.
Spain was seen as a unified country by foreign powers – Henry VII, King of England saw Spain as united, and applied to both Ferdinand and Isabella when arranging a marriage for his son, Arthur, to Katherine of Aragon. However, this could merely have been because both of them were Katherine’s parents. On the other hand, Isabella and Ferdinand were also both rulers in this own right and so it made sense to apply to both of them. Possibly Spain was seen as a unified country this early on because foreign powers knew that it would be, either under their son or grandson.
Something which did unite Spain was the Inquisition and religion in general. All areas of Spain, after the conquer of Granada, had the same religion, and this began to be enforced by the Spanish Inquisition, who also dealt with accusations of witchcraft. The Inquisition acted across the whole of Spain as a united front, even if they were also run locally within different areas of Spain. The Inquisition brought Spain together in a way.
Spain wasn’t United
Constitutionally the areas that made up Spain (Castile, Aragon, Catalonia and Valencia) were separate entities. They had their own opinions and views on things like the succession. Castile would accept a female heir to the throne, but Aragon wouldn’t, especially if she didn’t even have a male heir to succeed her. They were ruled by the same monarchs, but this was difficult when they were separate entities, and ruled from just one place over such a large area.
When Isabella died Castile wasn’t ruled by Ferdinand, who already ruled Aragon, but by their eldest surviving daughter, Juana (also known as Joanna). Juana was Isabella’s heir, not Ferdinand, although Ferdinand did rule in her name. Nevertheless, Juana was Queen of Castile even if Ferdinand did rule in her name during her madness, which meant that she couldn’t rule properly.
Francisco I Ximenez de Cisneros and the issue over the Archbishopric of Toledo was a clear sign of the separation of Castile and Aragon and of the different powers of Isabella and Ferdinand. Ferdinand wanted his illegitimate son to take the archbishopric when it became vacant in 1495, but Isabella instead appointed her own choice – her confessor, Francisco I Ximenez de Cisneros. Isabella had the final choice because the archbishopric was in Castile rather than Aragon, and this was one example where Isabella pushed her influence rather than accept her husband’s decision.
J. Edwards, ‘Ferdinand and Isabella’
William Hickling Prescott, ‘History of the Reign of Ferdinand and Isabella, the Catholic’
Geoffrey Woodward, ‘Spain in the Reigns of Ferdinand and Isabella 1474-1516’