On October 26, 1388, the Treaty of Bayonne was signed between King John I of Castile and John of Gaunt, Duke of Lancaster, who had claimed the Castilian throne through his marriage to Constance of Castile. The treaty resolved the succession dispute by recognizing John I as the legitimate king and providing for the marriage of John of Gaunt's daughter, Catherine of Lancaster, to John I's son and heir, Prince Henry. The agreement marked a reconciliation between the Trastámara dynasty and the English crown.

The Treaty of Bayonne was celebrated in Castilian poetry as a triumph of diplomacy, a peaceful resolution to a conflict that might have led to further warfare. The treaty's terms, including the marriage alliance, were praised by court poets who saw the union as a symbol of the unity of Christendom and the triumph of reason over ambition. The event also influenced the development of Spanish political poetry, which often engaged with themes of dynastic legitimacy, royal authority, and the role of diplomacy in maintaining peace.