The Anglo-Portuguese Alliance …

Years: 1384 - 1395

The Anglo-Portuguese Alliance and the Treaty of Windsor (1386–1387)

English support for the House of Avis during Portugal’s crisis of succession in the 1380s laid the foundation for a long-lasting alliance between Portugal and England, shaping Portuguese foreign policy for the next five centuries.

The Treaty of Windsor (May 1386)

In May 1386, the Treaty of Windsor formally confirmed the Anglo-Portuguese alliance, which had been forged through English aid at the Battle of Aljubarrota (1385). The treaty established a "pact of perpetual friendship", guaranteeing mutual military and commercial cooperation between the two kingdoms. It remains one of the oldest standing alliances in history.

John of Gaunt’s Castilian Campaign (1387)

In 1387, John of Gaunt, Duke of Lancaster, son of Edward III of England and father of Henry IV, launched an expeditionary campaign in Galicia, seeking to press his claim to the Castilian throne with Portuguese support.

  • Despite his military presence, Gaunt failed to gain the support of the Castilian nobility, who remained loyal to the rival claimant, King John I of Castile.
  • Unable to secure his objective, Gaunt negotiated a settlement and returned to England with a cash compensation, effectively ending his campaign.

Although the Castilian venture did not succeed, the Anglo-Portuguese alliance endured, providing Portugal with a powerful ally in its struggles against Castile and securing key commercial and military advantages for centuries to come.

 

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