The Brittany War of Succession (1341-1364) was a conflict in the region of Brittany, France, over the rightful heir to the duchy after the death of Duke John III. The war primarily involved two claimants: Charles of Blois, supported by the French crown, and Jean de Montfort, backed by the English crown. This struggle was part of the larger context of the Hundred Years' War. The conflict saw numerous battles and shifting alliances, leading to significant devastation in Brittany. Ultimately, the war concluded with the Treaty of Guérande in 1365, which recognized Jean de Montfort as the Duke of Brittany, solidifying English influence in the region.