The Castilian Civil War began in 1366, a dynastic struggle between King Pedro I of Castile and his half-brother, Henry of Trastámara, for the throne of Castile. The conflict quickly became entangled with the Hundred Years' War, as Pedro sought English support while Henry received backing from France. The war would culminate in Henry's victory and Pedro's death in 1369, fundamentally altering the political landscape of the Iberian Peninsula and shifting the balance of power between England and France.

The Castilian Civil War was a transformative event for Spanish literature, inspiring a rich body of chronicles, ballads, and epic poetry that recounted the struggle between the rivals. The figure of Pedro the Cruel (Pedro el Cruel) became a stock character in Spanish literature, representing the archetype of the tyrannical king, while Henry of Trastámara was celebrated as the righteous defender of the realm. These literary treatments, including the famous ballads of the 'Romancero', helped shape the historical memory of the conflict and influenced later Spanish poets such as Lope de Vega and Calderón de la Barca.