The Treaty of Guérande (April 12, 1365):…

1365 CE

The Treaty of Guérande (April 12, 1365): The End of the Breton War of Succession

On April 12, 1365, the First Treaty of Guérande formally ended the Breton War of Succession (1341–1364) and established John IV de Montfort as the Duke of Brittany. The treaty settled the long-standing dispute between the Montfort and Penthièvre factions, while also securing French royal recognition for John’s rule.

Terms of the Treaty

John IV de Montfort was officially recognized as Duke of Brittany.
The Penthièvre family was not entirely excluded from succession:
- The Duchy of Brittany would pass through the male line of the Montfort family.
- If the Montfort line died out, the title would pass to the Penthièvre family’s male heirs.
Joan of Penthièvre, widow of Charles of Blois, retained:
- The Prerogative of Penthièvre (her family’s noble status).
- The Viscountcy of Limoges, ensuring her family’s continued wealth and influence.

Why Did Charles V Accept the Treaty?

King Charles V of France did not oppose John IV’s elevation to duke, despite Montfort’s previous English support, for several reasons:

Preventing an English Alliance
- John IV had once been a protégé of Edward III of England, and there was a risk that he might declare full allegiance to England.
- Edward’s daughter Mary, John IV’s first wife, had died in 1361, leaving Brittany’s political alignment uncertain.
- By recognizing John IV as duke, Charles V secured his loyalty and prevented a potential English stronghold in Brittany.
France’s Weakness in the Hundred Years’ War
- France was militarily and financially exhausted due to the ongoing Hundred Years’ War.
- Mercenary bands (routiers) still roamed the countryside, making another campaign in Brittany unfeasible.
Winning the Support of the Breton Nobility
- By accepting John IV’s oath of loyalty, Charles V ensured the friendship of the Breton nobility, strengthening France’s political control over the region.

Impact and Legacy

The Treaty of Guérande (1365) firmly established Montfort rule in Brittany, but tensions between Brittany and France remained unresolved.
John IV remained largely autonomous, balancing his allegiance between France and England.
The Penthièvre family’s conditional succession rights would later fuel future conflicts, including the War of the Breton Succession (second phase) in 1420.
By recognizing John IV, Charles V stabilized the region temporarily, allowing France to focus on rebuilding its strength in the Hundred Years’ War.

The Treaty of Guérande (1365) successfully ended decades of civil war in Brittany, securing Montfortist rule while preserving the Penthièvre family's status, ensuring that Brittany remained a key political player in medieval France.