The Spanish expedition immensely increased the Black Prince's difficulties. He exhausted his finances to equip his army, and both on their coming and going his soldiers cruelly pillaged the country. Edward now dismissed most of his troops and urged them to betake themselves to France. In January, 1368, he obtained from the estates of Aquitaine a new hearth tax of ten sous a hearth for five years. The tax was freely voted and collected from the great majority of the payers without trouble. The towns were mainly exempt from it by reason of their liberties; and the lesser lords were as yet not averse from English rule. But the greater feudatories saw in the new hearth-tax a pretext for revolt. They had no special zeal for the French monarchy, but the house of Valois was weak and far removed from their territories. Their great concern was the preservation of their independence, which seemed more threatened by a resident prince than by a distant overlord at Paris. Even before the imposition of the hearth-tax, the Count of Armagnac entered into a secret treaty with Charles V., who promised to increase his territories and respect his franchises, if he would return to the French allegiance. The lord of Albret married a sister of the French queen and followed Armagnac's lead. A little later the Counts of Périgord and Comminges and other lords associated themselves with this policy. Thus the rule of the Black Prince in Aquitaine, acquiesced in by the mass of the people, was threatened by a feudal revolt. Armagnac appealed to the parliament of Paris against the hearth-tax. Charles V. accepted the appeal on the ground of the non-exchange of the renunciations which should have followed the treaty of Calais. Cited before the parliament in January, 1369, the Black Prince replied that he would go to Paris with helmet on head and with sixty thousand men at his back. His father once more assumed the title of King of France, and war broke out again.
The relative positions of France and England were different from what they had been nine years before. Edward III. was sinking into an unhonoured old age, and the Prince of Aquitaine suffered from dropsy, and was incapable of taking the field. Of their former comrades some, like Walter Manny, were dead, and others too old for much more fighting. On the other side was Charles V., who had tamed Navarre and the feudal lords, had cleared the realm of the companies, had put down faction and disorder, and had made himself the head of a strong national party, resolved to effect the expulsion of the foreigner. His chief military counsellors were Du Guesclin, and Du Guesclin's old adversary in the Breton wars, Oliver de Clisson, now the zealous servant of the king. A wonderful outburst of French patriotism facilitated the reconquest of the lands that had passed to English rule nine years before. Even the tradition of military superiority availed little against commanders who were learning by their defeats how to meet their once invincible enemies.
There was a like modification in the foreign alliances of the two kingdoms. Dynastic changes in the Netherlands had robbed Edward of supporters who, though costly and ineffective, had been imposing in outward appearance. Even after the dissolution of the alliances of the early years of the war, the temporising policy of Louis de Male at least neutralised the influence of Flanders. During the peace both Edward and Charles did their best to win the goodwill of the Flemish count. Louis' relation to the two rivals was the more important since his only child was a daughter named Margaret. In 1356, this lady, to Edward's great disgust, was promised in marriage to Philip de Rouvre, Duke and Count of Burgundy, and Count of Artois. The death of Philip in 1361 saved Edward from the danger of a great state with one arm in the Burgundies and the other in Flanders and Artois; and the irritation of Louis de Male at Charles V.'s grant of the Burgundian duchy to his youngest son, Philip the Bold, gave the English king a new chance of winning his favour. At last, in 1364, Edward concluded a treaty with Flanders according to his dearest wishes. Edmund of Langley, Earl of Cambridge, his youngest son, was betrothed to the widowed Margaret, with Ponthieu, Guînes, and Calais as their appanage. Great as were Edward's sacrifices, they were worth making if a permanent union could be established between England and Flanders, equally threatening to France and to the lords of the Netherlands. Charles persuaded Urban V. to refuse the necessary dispensations for the marriage. Edward and Louis, irritated at the success of this countermove, waited patiently and renewed their alliance.
No sooner was his understanding with Armagnac completed than Charles strove to secure the support of northern as well as of southern feudalism against Edward. He offered his brother, Philip of Burgundy, to Margaret, along with the restoration of the districts of French Flanders, which he still held. In June, 1369, the marriage took place. Edmund of Cambridge lost his last chance of the great heiress, and Charles V. bought off the enmity of the Count of Flanders at the price of that union of Burgundy and Flanders which, in the next century, was to make the descendants of Philip and Margaret the most formidable opponents of the French monarchy. For the moment, however, Charles gained little. Flemish ships, indeed, fought against the English at sea, notably in Bourgneuf Bay in 1371, but next year Louis made peace with them. Despite his daughter's marriage, the Count of Flanders still showed that his sympathies were with England. The other princes of the Netherlands were much more decidedly on the French side than the Count of Flanders. Margaret of Hainault, Queen Philippa's sister, had, after the death of her husband the Emperor Louis of Bavaria, in 1347 fought with her son William for the possession of her three counties of Hainault, Holland, and Zealand, to which Philippa also had pretensions, naturally upheld by her husband. William obtained such advantages over his mother that Margaret was obliged to invoke the assistance of her brother-in-law. Eager to regain his influence in the Netherlands, Edward willingly agreed to be arbiter between Margaret and her son, and at his suggestion the disputed lands were divided between them. William was married to Maud of Lancaster, Duke Henry's elder daughter, and thus secured to the English alliance. On Margaret's death William inherited all the three counties: but Maud died, and William became insane, whereupon his brother and heir invoked the support of the Emperor Charles IV., and was duly established in his fiefs. The claims of Philippa were ignored, and the Lancaster marriage with the lord of Holland, like the projected union of Edmund with the heiress of Flanders, failed to fulfil Edward's hopes.
Meanwhile Edward had to face the constant hostility of the emperor. Wenceslaus of Luxemburg, brother of Charles IV., had married the daughter and heiress of John III of Brabant, with the result of solidly establishing the house of Luxemburg in the strongest of the duchies of the Low Countries. With the Luxemburger as with the Bavarian, Edward's relations were unfriendly. Two only of the Low German lords, the dukes of Gelderland and Jülich, were willing to take his pay. Early in the war they were assailed by the Luxemburgers, and the contest occupied all their energies. Thus Edward re-entered the struggle against France with no help save that of his own subjects. Urban V. died at Avignon in 1370, and his successor, Gregory XI., was as little friendly to English claims in France as his predecessors had been. Pope, emperor, and the Netherlandish princes, were all either French or neutral. And in 1369 Peter of Castile lost his throne, and soon afterwards perished at his brother's hands. Henry of Trastamara, henceforth King of Castile, became the firm ally of the French, who had already the support of Aragon. Even Charles the Bad thought it prudent to declare for France.
At each stage of the war the French took the initiative. The appeal of the southern nobles was the beginning of a national movement which, before March, 1369, was supported by more than 900 towns, castles, and fortified places in Edward's allegiance. In April the French invaded Ponthieu and were welcomed as deliverers at Abbeville and the other towns of the county. John of Gaunt led an army during the summer from Calais southwards. He marched through Ponthieu, crossed the Somme at Blanchetaque, and ravaged the country up to the Seine. Then he retired exhausted, having gained no real advantage by this mere foray. Charles announced that, as Edward had supported the free companies, he fell under the excommunication threatened by the pope against the abettors of these pests of society, and that the vassals of the English crown were therefore relieved from allegiance to him. Soon afterwards he declared that Edward had forfeited all his possessions in France.
Quercy and Rouergue, which had submitted last, were the first districts of Aquitaine to revolt. Cahors declared for France as soon as the Black Prince was cited to Paris. By the end of 1369 all Quercy had acknowledged Charles V., and John of Armagnac ruled Rouergue as his vassal. It was the same in the Garonne valley, where towns which had no quarrel with English rule, were swept away by the strong tide of national feeling that surged round their walls. A systematic attack was made upon the English power in Aquitaine. Charles V. fitted out new armies in which the townsmen and the country-folk fought side by side with the nobility. Two of his brothers, John, Duke of Berri, and Louis, Duke of Anjou, prepared to assail the intruders, Berri in the central uplands, Anjou in the Garonne valley. It was not enough to recover what was lost. Aggression must be met by aggression, and the Duke of Burgundy, Charles' third brother, equipped a fleet in Norman ports, either to invade England or at least to cut off the Black Prince from his base. Portsmouth was burnt, before England had made any effort to defend her shores.
The English were strangely inactive. The Black Prince lay sick at Cognac, and of his subordinates Chandos, now seneschal of Poitou, alone showed vigour. Chandos, finding the lords of Poitou much more loyal to the English connexion than those of the south, was able to take the aggressive by invading Anjou. He was, however, soon recalled to protect Poitou, and on January 1, 1370, was mortally wounded at the bridge of Lussac. James Audley had already died of disease in another Poitevin town. While England was losing her best soldiers, Du Guesclin began a fresh series of raids in the Garonne valley. Soon the banner of the lilies waved within a few leagues of Bordeaux, and ancient towns of the English obedience, like Bazas and Bergerac, fell into the enemy's hands. With the capture of Périgueux, the Limousin was isolated from Gascon succour. In August the Duke of Berri appeared before the walls of the cité, or episcopal quarter, of Limoges, and the bishop promptly handed it over to him.
Disasters at last stirred up the English to action. In 1370 John of Gaunt was sent with one army to Gascony and Sir Robert Knowles with another to Calais. The Black Prince, though unable to ride, was eager to command. It was arranged that while Lancaster led one force from Bordeaux to Limoges, Edward should accompany another that marched from Cognac towards the same destination. To resist this combination Du Guesclin strove to combine the separate armies of the Dukes of Anjou and Berri. However, he failed to prevent the junction of Lancaster and Edward, and their advance to Limoges. On September 19, the anniversary of Poitiers, the city of Limoges opened its gates after a five days' siege. The English took a terrible revenge. Not a house in the cité was spared, and the cathedral rose over a mass of ruins. The whole population was put to the sword, the Black Prince in his litter watching grimly the execution of his orders. A few gentlemen alone were saved for the sake of their ransoms. Among them was the brother of Pope Gregory XI., who not unnaturally became a warm friend of the patriotic party. The sack of Limoges was the last exploit of the Black Prince. Early in 1371, he returned to England, partly because of his state of health, and partly because he had no money to pay his soldiers. It is not unlikely that he was already on bad terms with John of Gaunt, who had necessarily taken the chief share in the campaign and was nominated his successor. Too late, efforts were made to conciliate the Gascons; in 1370 a supreme court was set up at Saintes to save the necessity of appeals to London which had become as onerous as the ancient frequency of resort to the parliament of Paris; and the hearth-tax, the ostensible cause of the rising, was formally renounced.
Sir Robert Knowles's expedition of 1370 was as futile as that of Lancaster. He advanced from Calais into the heart of northern France. Taught by long experience the danger of joining battle, the French allowed him to wander where he would, plundering and ravaging the country. Roughly following the line of march of Edward III. in 1360, the English advanced through Artois and Vermandois to Laon and Reims, and thence southwards through Champagne. Then striking northwards from the Burgundian border, they appeared, at the end of September, before the southern suburbs of Paris. To dissipate the alarm felt at the presence of the English, Du Guesclin was summoned from the south and made constable of France. Before his arrival Knowles had moved on westwards 'towards the Beauce, intending to reach his own estates in Brittany for winter quarters. But his young captains got out of control. Led by a Gloucestershire knight, Sir John Minsterworth, "ready in hand but deceitful and perverse in mind," a considerable section of the troops refused to follow the old "tomb-robber" to Brittany, and determined to spend the winter where they were, under Minsterworth's leadership. Knowles would not give place to his subordinate, and made his way to Brittany with the part of his army which was still faithful to him. No sooner was he well started than Du Guesclin, after a march of ninety miles in three days, fell upon his rearguard at Pontvallain in southern Maine and overwhelmed it on December 4, 1370. Knowles managed to reach Brittany with the bulk of his forces, and Minsterworth, the real cause of the disaster, ventured to go to England and denounce his leader as a traitor. He was forced to flee to France, where he openly joined the enemy. Seven years later he was captured and executed.