Brittany, entered the service of Charles and became one of his most successful generals. 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. Du Guesclin succeeded in his object; Henry of Trastámara was placed on the Castilian throne. Having been opposed by the French, Pedro appealed to the Black Prince for aid, promising rewards. The Black Prince succeeded in restoring Pedro following the Battle of Nájera. But Pedro refused to make payments, to the chagrin of his English and Navarrese allies. Without them, Pedro was once more deposed, and lost his life. Again the English gained nothing from their intervention, except the enmity of the new king of Castile, who allied himself with France. The English merchant community that had been established in Seville was massacred on Henry's order. Between 1372 and 1380, Castilian corsairs raided the southern coasts of England with relative impunity, turning the tide in the Hundred Years' War decisively in France's favour. 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. Unheeded, they turned to the King of France as their feudal overlord. But by the Treaty of Brétigny the King of France had lost his suzerainty over Aquitaine. After reflecting on the matter, it was asserted that Edward III's renunciation of France had been imperfect. In consequence, the King of France retained his suzerainty over Aquitaine. 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. French recovery When Charles V resumed the war, the balance had shifted in his favour; France remained the largest and most powerful state in Western Europe and England had lost its most capable military leaders. Edward III was too old, the Black Prince an invalid, while in December 1370, John Chandos, the vastly experienced seneschal of Poitou, was killed in a skirmish near Lussac-les-Châteaux. On