The Failure of John of Gaunt’s Castilian…

The Failure of John of Gaunt’s Castilian Campaign (1387) and His Treaty with Castile

By 1387, John of Gaunt’s long-anticipated invasion of Castile, launched in April, had collapsed into failure, plagued by disease, logistical issues, and ineffective military strategy.

The Struggles of the Invasion (April–June 1387)

• John’s army was already weakened—many of his troops had succumbed to sickness before the campaign even began.
• His English forces were far outnumbered by their Portuguese allies, reducing his ability to wage an effective offensive.
• The Castilians, led by John I of Castile, refused to offer pitched battle, instead using harassment tactics carried out by French mercenaries.
• The Galician-Anglo-Portuguese troops were forced to rely on foraging in the arid Spanish landscape, leading to severe food shortages.

The Campaign’s Collapse

• The campaign became bogged down in time-wasting sieges of fortified towns, failing to achieve any major victories.
• Hundreds of English troops, including John of Gaunt’s personal friends and retainers, died from disease and exhaustion.
• Desertions increased, and many English knights abandoned the campaign, negotiating safe passage through France to return home.
• By June 1387, the army had returned to Portugal, exhausted and demoralized.

The Treaty of Bayonne: John of Gaunt Renounces His Claim to Castile

• Shortly after the campaign’s failure, John of Gaunt entered into secret negotiations with John I of Castile.
• In the Treaty of Bayonne (1388), the following terms were agreed upon:
  • John of Gaunt and his wife, Constance of Castile, formally renounced their claim to the Castilian throne.
  • In return, Gaunt received a large annual payment from the Castilian crown.
  • Catherine of Lancaster, Gaunt’s daughter, was betrothed to Henry III of Castile, the son of John I of Castile, ensuring dynastic reconciliation between the rival Castilian factions.

Aftermath and Legacy

• The failed campaign marked the end of John of Gaunt’s ambitions in Spain, forcing him to return to England.
• His daughter Catherine’s marriage to Henry III of Castile helped unify the Trastámara dynasty, ensuring stability in Castile.
• The Anglo-Portuguese alliance remained strong, leading to the Treaty of Windsor (1386), which solidified the long-standing alliance between England and Portugal.

John of Gaunt’s Castilian adventure, once a grand ambition to claim a kingdom, ended in humiliating failure, but his diplomatic maneuvering secured peace with Castile and ensured that his family remained influential in Iberian politics for generations to come.