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
Pomeranian War Frederick's downfall and to humiliate and destroy the Swedish queen Louisa Ulrika of Prussia, Frederick's sister. The Hats faction was also encouraged to declare war by France, whose wishes were central to the Hats' actions. Frederick's invasion of Saxony in 1756 was used as a pretext for war, being denounced by both Sweden and France as a violation of the Treaty of Westphalia of 1648, of which they were both guarantors. On March 21, 1757 the governments of France and Austria agreed a convention in which Sweden and France explained that they had to maintain Germany's freedom in line with