Westphalia to be Catholic. Osnabrück was divided almost equally between Catholicism and Protestantism. Parts of Westphalia came under Brandenburg-Prussian control during the 17th and 18th centuries, but most of it remained divided by duchies and other areas of feudal power. The Peace of Westphalia of 1648, signed in Münster and Osnabrück, ended the Thirty Years' War. The concept of nation-state sovereignty resulting from the treaty became known as "Westphalian sovereignty". After the defeat of the Prussian Army by the French at the Battle of Jena–Auerstedt, the Treaty of Tilsit in 1807 made the easternmost portion of today's Westphalia part of the
Battle of the Dunes (1658) The victory at the Battle of the Dunes and its consequences would lead to the end of ten years of war with the signing of Treaty of the Pyrenees. By this treaty France gained Roussillon and Perpignan, Montmédy and other parts of Luxembourg, Artois and towns in Flanders, including Arras, Béthune, Gravelines and Thionville, and a new border with Spain was fixed at the Pyrenees. The 1659 treaty also required the Spanish king to recognise and confirm all French gains in the 1648 Peace of Westphalia. The defeat of the Spanish relief force and the taking of Dunkirk ended the