With the election of Walther von Supersax of Conches as bishop in 1457, the German-speaking part of the valley finally won the supremacy. At the outbreak of the Burgundian War in 1475 the bishop of Sion and the Zenden made a treaty with Bern. In November of the same year they seized all Lower or Savoyard Valais up to Martigny. In March 1476, after the victory of Grandson, they advanced and captured St Maurice, Évian, Thonon and Monthey. They had to give up the last three districts in 1477, but won them again in 1536. In the treaty of Thonon in 1569, Monthey, Val-d'llliez and Le Bouveret were permanently annexed to Valais. These conquered districts in the Lower Valais were ruled as subject lands by the bishop and the Tithings of the Upper Valais until 1798. On March 12, 1529, Valais became an associate member ("Zugewandter Ort") of the Swiss Confederation.