The Portuguese Advance in the Castilian Succession War (1475)

After Afonso V of Portugal and Joanna la Beltraneja were proclaimed sovereigns of Castile in Plasencia on May 25, 1475, the Portuguese army marched towards Arévalo, intending to continue toward Burgos, a strategic city in the conflict.

Strategic Importance of Burgos

• Afonso V hoped to unite with troops sent by his ally, Louis XI of France, reinforcing his army against Isabella and Ferdinand.
• However, Burgos was divided:
  • The castle of Burgos was held by the Estúñiga family, who supported Joanna la Beltraneja.
  • The city itself was controlled by the Fernández de Velasco family, loyal to Isabella of Castile.

Portuguese Strategy and Challenges

• Afonso’s next move depended on securing support from Castilian noble factions, particularly in Burgos, which was a vital stronghold.
• Despite the loyalty of the Estúñigas, the Portuguese advance faced resistance from Isabella’s supporters.

Outcome: Afonso’s Difficulties in Securing Castilian Support

• The war did not unfold as Afonso V had expected. His military movements were slow, and Castilian nobles who had initially supported Joanna became increasingly hesitant.
• This hesitation, combined with Isabella’s consolidation of power in key cities, made it difficult for Afonso to sustain his campaign.

The struggle for Burgos and northern Castile was part of the broader War of the Castilian Succession (1475–1479), which ultimately resulted in Isabella and Ferdinand’s triumph, while Afonso failed to secure Castile for Joanna.