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
Siege of Breda (1624) thereafter. The siege of 1624 captured the attention of European princes and, along with other battles like White Mountain (1620), played a part in the Spanish army regaining the formidable reputation it had held throughout the previous century. In the latter stages of the combined Eighty and Thirty Years' wars that had greatly strained Spanish resources, Breda was lost to the Dutch under Frederick Henry after a four-month siege. In the 1648 Treaty of Westphalia that ended the Thirty and Eighty Years' wars, it was ceded to the Dutch Republic. There were several motives for Spinola's siege of Breda. Because