The War of the Castilian Succession (1475-1479) was a conflict in Spain over the rightful heir to the throne of Castile. It began after the death of Henry IV of Castile, whose daughter, Joanna, was contested by her half-sister, Isabella. The war saw various factions supporting either Joanna or Isabella, leading to a struggle for power. The conflict involved significant battles and alliances, with Aragon and Portugal playing crucial roles. Ultimately, Isabella emerged victorious, solidifying her claim to the throne and paving the way for the unification of Spain under her and her husband, Ferdinand II of Aragon.