War of the Breton Succession
In 1341, conflict over the succession to the Duchy of Brittany began the War of the Breton Succession, in which Edward backed John of Montfort and Philip backed Charles of Blois. Action for the next few years focused around a back-and-forth struggle in Brittany. The city of Vannes in Brittany changed hands several times, while further campaigns in Gascony met with mixed success for both sides. The English-backed Montfort finally succeeded in taking the duchy but not until 1364.