John of Gaunt’s Withdrawal from Castile and the Anglo-Portuguese Alliance (1388)

After his unsuccessful invasion of Castile, John of Gaunt, Duke of Lancaster, formally abandoned his claim to the Castilian throne in 1388, concluding peace at Bayonne in exchange for a substantial financial settlement from King John I of Castile. At the same time, his dynastic ambitions shifted to Portugal, as his daughter, Philippa of Lancaster, married King John I of Portugal, solidifying an Anglo-Portuguese alliance.

Additionally, the informal truce between Castile and Portugal (established in 1387) was extended, allowing time for an official peace treaty to be arranged between the Iberian kingdoms.

Key Developments Leading to the 1388 Peace Agreement

1. John of Gaunt’s Invasion of Castile (1386–1387) and Failure

   • Gaunt had asserted a claim to the Castilian throne through his marriage to Constance of Castile, daughter of the deposed King Peter I ("the Cruel").
   • His military campaign in Castile (1386–1387), launched in alliance with Portugal, failed to gain significant ground.
   • Facing logistical difficulties, lack of local support, and superior Castilian resistance, he withdrew from the campaign.

2. Marriage of Philippa of Lancaster and John I of Portugal (1387)

   • Seeking to secure a lasting alliance with Portugal, Gaunt arranged for his daughter Philippa of Lancaster to marry King John I of Portugal.
   • This marriage strengthened Anglo-Portuguese ties and helped Portugal resist Castilian influence.

3. The Peace of Bayonne (1388): Gaunt Renounces Castile

   • Gaunt formally relinquished his claim to Castile, recognizing John I of Castile as the legitimate ruler.
   • In exchange, he received a large financial settlement, bringing an end to his unsuccessful Iberian ambitions.

4. The Extension of the Truce Between Castile and Portugal (1387–1388)

   • With Gaunt out of the picture, Castile and Portugal extended their truce, preparing for a lasting peace agreement.

Impact and Legacy

• John of Gaunt’s withdrawal from Castile ended English intervention in Castilian affairs, redirecting Gaunt’s focus to England and France.
• The marriage between Philippa of Lancaster and John I of Portugal established the Anglo-Portuguese Alliance, which would endure for centuries.
• The truce between Castile and Portugal paved the way for a formal peace treaty, reducing conflicts in the Iberian Peninsula.

The 1388 Peace of Bayonne marked the definitive end of John of Gaunt’s claim to Castile, while the Anglo-Portuguese marriage created a diplomatic bond that would influence European politics for generations.