The reasons why the treaty of Bretigny failed to give a permanent settlement of the quarrel between England and France were many. The English pleaded that the French never fulfilled their obligations, for King John found his people very unwilling to raise his huge ransom, and never paid half of it. He returned to England in 1364 to surrender himself in default of payment--for he had a keen sense of honour in such things--and then died. His son, Charles V., at once refused--as was natural--to pay the arrears. But a more fruitful source of quarrelling was the civil war in Brittany, which still lingered on after twenty years of fighting; English and French succours came to help the two rival dukes, and fought each other on Breton soil, though peace reigned elsewhere. The same thing was soon after seen in Spain: Pedro the Cruel, the wicked King of Castile, was attacked by his bastard brother, Henry of Trastamara, who enlisted a great host of French mercenaries, under Bertrand du Guesclin, the best professional soldier in France. Driven out of Castile by the usurper and his allies, Pedro fled to Bordeaux, where the Black Prince was reigning as Duke of Aquitaine. He enlisted the help of the English, who were jealous of French influence in Spain, and bought the aid of Edward's younger brothers, John of Gaunt, who was now a widower, and Edmund of Cambridge, by marrying his two daughters to them. Edward raised a great army of English and Gascons, and crossed the Pyrenees to restore King Pedro. At Najara[23] he routed the French and Castilians, took Bertrand du Guesclin prisoner, and drove Henry of Trastamara out of the land (1367). But the ungrateful Pedro then refused to repay the large sums which Edward had spent in raising his army, and the prince withdrew in wrath to Aquitaine. He took back with him an intermittent fever which he had caught in Spain, and never recovered his health. Left to his own resources, Pedro was soon beset for a second time by his brother and the French; he was captured by treachery, and slain by Henry of Trastamara's own hand. [Sidenote: =Rebellion in Aquitaine.--Massacre at Limoges.=]