The Failure of John of Gaunt’s Castilian …

Years: 1387 - 1387

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.

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Southwest Europe (1387 - 1387)
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Atlantic Southwest Europe (1387 - 1387)

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