Caroline phaseBrittany, France
In the Treaty of Brétigny, Edward III renounced his claim to the French throne in exchange for the duchy of Aquitaine in full sovereignty. Between the nine years of formal peace between the two kingdoms, the English and French clashed in Brittany and Castile. In 1364, John II died in London, while still in honourable captivity. Charles V succeeded him as king of France.
In the War of the Breton Succession, the English backed the heir male, the House of Montfort (a cadet of the House of Dreux, itself a cadet of the Capetian dynasty) while the French backed the heir general, the House of Blois.
With peace in France, the mercenaries and soldiers lately employed in the war became unemployed, and turned to plundering. Charles V also had a score to settle with Pedro the Cruel, King of Castile, who married his sister-in-law, Blanche of Bourbon, and had her poisoned. Charles V ordered Du Guesclin to lead these bands to Castile to depose Pedro the Cruel. The Castilian Civil War ensued. Having been opposed by the French, Pedro appealed to the Black Prince for aid, promising rewards.
The Black Prince's intervention in the Castilian Civil War, and the failure of Pedro to reward his services, depleted the prince's treasury. He resolved to recover his losses by raising the taxes in Aquitaine. The Gascons, unaccustomed to such taxes, complained. Charles V summoned the Black Prince to answer the complaints of his vassals but Edward refused. The Caroline phase of the Hundred Years' War began.