Henry IV of Castile

Henry IV of Castile signed the Treaty of the Bulls of Guisando, recognizing his half-sister Isabella as his legitimate heir instead of his daughter Joanna. This agreement was intended to resolve the succession dispute, but Henry later repudiated it, leading to renewed conflict.

After Henry IV's death, a civil war erupted between supporters of his daughter Joanna la Beltraneja and those of his half-sister Isabella. The war involved Portuguese and Aragonese intervention and ended with Isabella's victory, securing her throne and leading to the union of Castile and Aragon.

During the War of the Castilian Succession, Henry IV's forces lost control of the Canary Islands to Portuguese-backed rebels. The islands were later recovered by Isabella I, but the conflict highlighted the weakness of Henry's reign and the erosion of royal authority.