1341–1343: War of Breton Succession, Another Front

The Hundred Years’ War opens indirect fronts. In Brittany, a dynastic crisis becomes a civil war, then a Franco-English theater: the stake is strategic, for controlling Breton ports means weighing on the Channel and communications.

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👑 April 30, 1341: Death of John III, Two Claimants

On April 30, 1341, Duke John III of Brittany dies without descendants, despite three marriages, and without naming a successor. Two camps form:

• Jane of Penthièvre, daughter of Guy of Penthièvre, wife (since 1337) of Charles of Blois, relative of the King of France;
• John of Montfort, half-brother of John III, Count of Montfort‑l’Amaury, pushed by his wife Joan of Flanders.

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🏰 1341: Coup de Main of John of Montfort

Fearing a verdict favorable to Charles of Blois, John of Montfort takes preemptive action: he installs at Nantes and seizes the ducal treasury. He attempts to obtain recognition of his legitimacy, but part of the nobility hesitates, for many seigneurs also possess lands in France and fear confiscation.

In June‑July 1341, John of Montfort leads a chevauchée to control strongholds (Rennes, Vannes, Brest, Dinan, etc.) and obtains about twenty places.

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🛡️ Autumn 1341: French Intervention and Fall of Nantes

After liegely rendering homage to Edward III, Charles of Blois must be put in possession of the dukedom. Philip VI assembles an army and entrusts the expedition to John the Good, Duke of Normandy, accompanied notably by Miles of Noyers and Charles of Blois.

The army marches on Nantes: after the taking of key positions, the town capitulates in early November 1341. John of Montfort surrenders on November 21, 1341, and relinquishes the capital. Sent to Paris, he is arrested and imprisoned at the Louvre in December 1341.

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🔥 1342–1343: Joan of Flanders and English Intervention

The Montfortist party might have collapsed, but Joan of Flanders relaunches resistance. Entrenched at Hennebont, she sends her son to England and concludes an alliance with Edward III in January 1342. The first reinforcements arrive, then a larger contingent disembarks at Brest in August 1342, fixing durably an English presence.

A truce is signed on January 19, 1343 (Truce of Malestroit). The conflict is not settled: it prolongs and contributes to installing England in Brittany, while destabilizing the region.

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🧠 Key Points to Remember

• 1341: a dynastic crisis becomes a Franco-English war by proxy.
• Brittany opens a strategic front on the Channel.
• 1343: the truce suspends, without resolving, a lasting conflict.