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
Duchy of Limburg Eighty Years' War, ended by the 1648 Peace of Westphalia. An area known as Limburg of the States, consisting of parts of Overmaas (but no part of the Duchy of Limburg itself), was ceded to the Dutch Republic. In 1661, the Dutch and the Spanish agreed on a re-partition of the county of Dalhem. The duchy of Limburg itself remained undivided under Spanish Habsburg rule as part of the Southern Netherlands, passing to the Austrian Habsburgs under the Treaty of Utrecht in 1713. When the region was occupied by the French in 1794, the Austrian duchy of Limburg proper was