The War of Castile's Throne, fought in the late 14th century, was a significant conflict involving claims to the Castilian throne between the English prince Edward, the Black Prince, and the Trastámara family, particularly Peter I of Castile. Following the death of King Alfonso XI, Peter I, supported by the Trastámara faction, ascended the throne. However, Peter’s brutal reign led to his eventual overthrow by his half-brother, Henry of Trastámara, supported by the rebellious factions in Castile.