Margraviate of Brandenburg fief of the Polish–Lithuanian Commonwealth, to which the electors paid homage. The electors of Brandenburg spent the next two centuries attempting to gain lands to unite their separate territories (the Mark Brandenburg, the territories in the Rhineland and Westphalia, and Ducal Prussia) to form one geographically contiguous domain. In the Peace of Westphalia ending the Thirty Years' War in 1648, Brandenburg-Prussia acquired Farther Pomerania and made it the Province of Pomerania by the Treaty of Stettin (1653). In the second half of the 17th century, Frederick William, the "Great Elector", developed Brandenburg-Prussia into a major power. The state constructed Brandenburg's
League of the Rhine of the 1648 treaty of Westphalia, the treaty which had made the League possible by authorising the German princes, immediate vassals of the Emperor, to conclude alliances between themselves or with foreign states. On August 14, 1658, the League of the Rhine was formed by: The League fielded a force of 6000 to fight on the side of France and the Empire against the Ottomans, seeing action in the 1664 Battle of Saint Gotthard. The League was promulgated to last for three years, and this was later twice extended. It officially ended in August 1667, its end should in fact