The dynasty that seized Castile in a civil war and, through the marriage of Isabella and Ferdinand, united the Spanish crowns.
The dynasty was born of civil war. Henry of Trastámara, illegitimate son of Alfonso XI of Castile, rebelled against his half-brother King Peter — remembered as "the Cruel" or "the Just" depending on the teller — in a struggle that drew in the wider Hundred Years’ War, with England backing Peter and France backing Henry.
The war turned when Henry, with the French mercenary captain Bertrand du Guesclin, killed Peter at Montiel in 1369 and took the throne as Henry II, founding the Trastámara line.
Henry II rewarded his noble backers so lavishly with lands and titles — the "Enrique of the largesses" — that he strengthened a great aristocracy his successors struggled to control. His son John I entangled Castile in the Portuguese succession, only to be crushed at the Battle of Aljubarrota in 1385, ending Castilian hopes of absorbing Portugal.
John I’s son Henry III the Sufferer, succeeding as a child, grew into a capable king who curbed the overmighty nobles and restored the authority of the crown before his early death.
The long reign of John II was dominated by his favourite, the constable Álvaro de Luna, who governed Castile for decades against the resistance of the high nobility before his dramatic fall and execution in 1453. It was a reign of factional struggle, cultural brilliance at court, and continued war against Granada.
John II’s daughter Isabella would inherit both the dynasty and its unfinished struggle to master the Castilian nobility.
A parallel branch of the Trastámaras had gained the crown of Aragon in 1412, so that by the fifteenth century the dynasty ruled both great Iberian kingdoms. The marriage in 1469 of Isabella of Castile to Ferdinand of Aragon — both Trastámaras — joined the two crowns in the persons of the "Catholic Monarchs".
Their joint reign, which completed the Reconquista at Granada in 1492 and sponsored Columbus, belongs to the dawn of the early modern era, but its dynastic foundation was the medieval House of Trastámara.