Without significant internal and foreign threats, John V reinforced ducal authority, reformed the military, constructed a coherent method of taxation, and established diplomatic and trade contacts with most of Western Europe.

He signed the Treaty of Troyes, which made Henry V heir to France, but he allowed his brother Arthur de Richemont to fight for the French.

Despite the military loss and the diplomatic treaty, the Counts of Penthièvre had not renounced their direct ducal claims to Brittany and continued to pursue them.

[2] Olivier, Count of Penthièvre and his mother, Margaret de Clisson, then spread rumours of his death and moved him to a new prison each day.

Some of its provisions were that John would abandon his commitments to the English, while Charles would dismiss his councillors who had advised him to support the Penthièvre revolt.

Initial Breton military support to Charles proved significant: in the Dauphin's Loire valley campaign in the summer of 1421, the duchy provided more than a third of his army, about the same as the Scots.

The duke of Brittany was convinced to do the same; by signing the Treaty of Saumur on 7 October 1425, John V once again allied with Charles, to which England responded with a formal declaration of war on 15 January 1426.

As a gesture of allegiance to the Anglo-French dual monarchy, he sent his younger and favourite son Gilles to England to grow up in Henry's household.

[6] Richemont would remain committed to the Dauphin's cause for the rest of the war, however, though John V's defection in 1427 contributed to the former's expulsion from the French court.

Even after the Anglo-Burgundian alliance ended in 1435, he remained formally aligned to the English cause, though in effect adopting a policy of careful neutrality, attempting to become friendly with the French and willing to broker a peace between both parties.

[4] However, John took part in the Praguerie revolt in 1440 against Charles VII, and signed a neutrality agreement on 11 July 1440 with the English, by which he promised not to give shelter to England's enemies.

Relations between England and Brittany eventually collapsed due to bad diplomacy and English raids into Breton territory in 1443 and 1449.

[7] By then, John V had already died, and his son and successor Francis I would subsequently pay homage to Charles VII on 16 March 1446, thereby formally ending any Breton support for the English.

John V married Joan of France, daughter of King Charles VI "the Mad" and his wife Isabeau of Bavaria.