The news of Pembroke’s defeat encouraged the French to attempt the conquest of Poitou.  Du Guesclin invaded the county from the north in co-operation with the Spaniards at sea, Owen of Wales abandoned the siege of Cornet castle, in Guernsey, which still held out against him, and hurried to join the Spaniards.  At Santander he met the captive Pembroke, and bitterly reproached the marcher earl with the part his house had taken in driving the Welsh from their lands.  In August Owen and the Spaniards were lying off La Rochelle.  Sir Thomas Percy, seneschal of Poitou, and the Captal de Buch were with a considerable force at Soubise, near the mouth of the Charente.  Owen ascended the river and fell unexpectedly on the English at night.  The English were utterly defeated and both leaders were taken prisoners, Thomas Percy, the future ally of Owen Glendower, being captured by one of Sir Owen’s Welsh followers.  Meanwhile, Du Guesclin, after receiving the surrender of Poitiers on August 7, pressed forward to the coast and was soon in touch with Owen and the Spaniards.  On the same September day Angouleme and La Rochelle opened their gates to the French.  In the course of the same month all the other towns of the district declared for the winning side.  The nobles of Poitou were still to some extent English in sympathy, and a considerable band of them and their followers took refuge in Thouars.  On December 1 this last stronghold of Poitevin feudalism surrendered.  The tidings of disaster roused the old English king to his final martial effort.  A fleet was raised and sailed from Sandwich, having on board the king, the Prince of Wales, the Duke of Lancaster, and many other magnates.  Contrary winds kept the vessels near the English coast, and the vast sums lavished on the equipment of the expedition were wasted.  In despair the Black Prince surrendered to his father his principality of Aquitaine.  When the king begged the commons for a further war subsidy, he was told that the navy had been ruined by his harsh impressment of seamen, and his refusal to give them pay when detained in port waiting for orders.  When the command of the sea passed to the French and their Spanish allies, all hope of retaining Aquitaine was lost.

The final stages in the ruin of the English power in France need not detain us long.  Despite his successes, Du Guesclin persevered in his policy of wearing down the English by delays and by avoiding pitched battles.  He turned his attention to Brittany, where Duke John, in difficulties with his subjects, had invoked the aid of an English army.  Thereupon the Breton barons called the French king to take possession of the duchy, whose lord was betraying it to the foreigner.  The old party struggle was at an end:  Celtic Brittany joined hands with French Brittany.  Before the end of 1373, Duke John was a fugitive, and only a few castles with English garrisons upheld his cause.  Of these Brest was the most important, and despite the Spaniards and Owen of Wales, the English were still strong enough at sea to retain possession of the place.