A dynastic struggle in Castile became a pivotal theater of the Hundred Years' War
The Castilian Civil War between 1351 and 1369 was far more than a local family feud. It drew in the superpowers of the era, England and France, transforming a struggle for the Castilian throne into a high-stakes geopolitical contest that reshaped the alliances of medieval Europe for decades to come.
The conflict erupted following the death of King Alfonso XI in March 1350, pitting the reigning monarch, Peter, against his illegitimate half-brother, Henry of Trastámara. Peter, known to his critics as 'The Cruel' and to his supporters as 'The Just,' was viewed by the nobility as a tyrant who aggressively expanded royal authority. His reign was marked by internal friction and a concurrent conflict with the Crown of Aragon, known as the War of the Two Peters.
Henry of Trastámara successfully leveraged widespread dissatisfaction among the upper nobility, securing crucial backing from France, Aragon, and the Papacy. By 1366, Henry had declared himself king at the monastery of Las Huelgas. Peter, forced to flee, sought refuge in English-held Gascony. He secured the aid of Edward, the Black Prince, by promising territorial concessions. This alliance proved decisive at the 1367 Battle of Nájera, where English forces helped Peter temporarily reclaim his throne. However, Peter's failure to honor his agreements with the English led to their withdrawal, leaving him vulnerable.
The final phase of the war saw Henry return with renewed French support, formalized by the 1368 Treaty of Toledo. This agreement secured French military aid in exchange for a Castilian fleet to assist in their ongoing struggles. In 1369, following the Battle of Campo de Montiel, Henry captured and murdered his brother. Ascending the throne as Henry II, he immediately purged Jews from high-ranking government positions and cemented Castile as a staunch French ally. This shift in allegiance significantly altered the balance of power in the broader Hundred Years' War, demonstrating how local succession crises could dictate the trajectory of continental conflicts.
Source: Castilian Civil War of 1351–1369
