Black Prince's chevauchée of 1355Bordeaux, France
A treaty to end the war was negotiated at Guînes and signed on 6 April 1354. However, the composition of the inner council of the French king, John II (r. 1350–1364), changed and sentiment turned against its terms. John decided not to ratify it, and it was clear that from the summer of 1355 that both sides would be committed to full-scale war. In April 1355 Edward III and his council, with the treasury in an unusually favourable financial position, decided to launch offensives that year in both northern France and Gascony. John attempted to strongly garrison his northern towns and fortifications against the expected descent by Edward III, at the same time as assembling a field army; he was unable to, largely because of a lack of money.
The Black Prince's chevauchée was a large-scale mounted raid carried out by an Anglo-Gascon force under the command of Edward, the Black Prince, between 5 October and 2 December, 1355. John, Count of Armagnac, who commanded the local French forces, avoided battle, and there was little fighting during the campaign. The Anglo-Gascon force of 4,000–6,000 men marched from Bordeaux in English-held Gascony 300 miles (480 km) to Narbonne and back to Gascony, devastating a wide swathe of French territory and sacking many French towns on the way. While no territory was captured, enormous economic damage was done to France; the modern historian Clifford Rogers concluded that "the importance of the economic attrition aspect of the chevauchée can hardly be exaggerated." The English component resumed the offensive after Christmas to great effect, and more than 50 French-held towns or fortifications were captured during the following four months.