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
War of the Fifth Coalition not been able to save Prussia. The Russian and French armies met in February 1807 at the savage and indecisive Battle of Eylau, which left behind between 30,000–50,000 casualties. Napoleon regrouped his forces after the battle and continued to pursue the Russians in upcoming months. The action in Poland finally culminated on 14 June 1807, when the French mauled their Russian opponents at the Battle of Friedland. The resulting Treaty of Tilsit in July ended two years of bloodshed and left France as the dominant power on the European continent. It also severely weakened Prussia and formed a Franco-Russian axis