The two principal claimants were Edward III of England, who derived his claim through his mother, Isabella, sister of Charles IV, and Philip, count of Valois, son of Philip IV's brother Charles. The assembly decided in favour of the count of Valois, who became king as Philip VI.
Edward III protested vigorously, threatening to defend his rights by every possible means. However, after his rival had defeated some Flemish rebels at the Battle of Cassel (August 1328), he withdrew his claim and did simple homage for Guyenne at Amiens in June 1329.
Philip responded with a demand for a declaration of liege homage and was, moreover, determined not to restore certain lands for which Edward had asked. War nearly broke out, and Edward was ultimately obliged to renew his homage, in private, on the French king’s terms (March–April 1331).
Anglo-French relations remained cordial for more than two years, but, from 1334 onward, encouraged by Robert III of Artois (grandson of Philip IV’s cousin), who had quarreled with Philip and had taken refuge in England, Edward seems to have regretted his weakness. He sought to recover the Gascon lands lost to Charles IV and demanded an end of the alliance between France and Scotland. He intrigued against Philip in the Low Countries and in Germany, while Philip, for his part, organized a small expedition to help the Scots (1336) and formed an alliance with Castile (December 1336). Both parties were preparing for war. Philip declared Guyenne confiscated on May 24, 1337, and in October Edward declared that the kingdom of France was rightfully his and sent a formal challenge to his opponent.
Hostilities in the Hundred Years’ War began at sea, with battles between privateers. Edward III did not disembark on the Continent until 1338. He settled at Antwerp and made an alliance (1340) with Jacob van Artevelde, a citizen of Ghent who had become the leader of the Flemish towns. These cities, in their anxiety to ensure the continued supply of English wool for their textile industries, had rebelled against Louis I, count of Nevers, who supported Philip. Edward also won the support of several rulers in the Low Countries, such as his brother-in-law William II, count of Hainaut, and John III, duke of Brabant. He also made an alliance (1338) with the Holy Roman emperor Louis IV (“the Bavarian”). Edward besieged Cambrai in 1339, and, on October 22 of that year, a French and an English army came within a few miles of each other at Buironfosse, without, however, daring to join battle.
A similar encounter occurred near Bouvines in 1340, after an English army supported by Flemish militia failed to take Tournai. Meanwhile, at sea, Edward’s ships defeated the French fleet, which had been reinforced by Castilian and Genoese squadrons, in the Battle of Sluis on June 24, 1340. This made it possible for him to move troops and provisions to the Continent. After this victory, the Truce of Espléchin (September 25, 1340), brought about by the mediation of Philip VI’s sister, Margaret, countess of Hainaut, and of Pope Benedict XII, temporarily suspended hostilities.