Brandenburg (bränˈdənbŏrk) [key], state (1994 est. pop. 2,540,000), c.10,400 sq mi (26,940 sq km), E Germany. Potsdam is the capital; other leading cities include Cottbus, Frankfurt-an-der-Oder, and Brandenburg. The state of Brandenburg consists of the former Prussian province of Brandenburg minus those parts of the province lying E of the Oder and Neisse rivers in Poland (see Germany). It became (1949) one of the states of the German Democratic Republic, was abolished as an administrative unit in 1952, and was reestablished as a state in 1990 shortly before the reunification of East and West Germany. Berlin is situated in, but is administratively separate from, Brandenburg. A 1996 referendum on whether to merge the two entities into a single state was approved by residents of Berlin but rejected by voters in Brandenburg.
Drained by the Havel, Spree, and Oder rivers, the region encompassed by the state has many lakes and pine forests. The Spree Forest, in Lower Lusatia, is inhabited by Slavic-speaking Wends, remnants of the population that inhabited Brandenburg at the time of its acquisition (12th cent.) by Albert the Bear. The Slavic principalities had been previously subdued by Charlemagne but had regained their independence. In the 10th cent. the German kings organized the North March, a small area on the Elbe, which was bestowed on Albert the Bear in 1134. Albert expanded his territory, and in 1150 he inherited the principality of Brandenburg from its last Wendish prince. The March of Brandenburg, as Albert's lands were called, were colonized by Germans and became Christianized. Albert's descendants, the Ascanians, ruled Brandenburg until their extinction in 1320.
Emperor Louis IV, a Wittelsbach, gave (1323) the vacant fief to members of his own house, but Emperor Charles IV (who confirmed the margraves of Brandenburg as electors of the Holy Roman Empire) forced the Wittelsbachs to surrender it and conferred (1373) it on his son Wenceslaus. When Wenceslaus became (1378) German king, Brandenburg went to his brother, later Emperor Sigismund, who in 1417 formally transferred it to Frederick I of the house of Hohenzollern. Among Frederick's early successors were Albert Achilles (reigned 1470–86), who introduced primogeniture as the law of inheritance of the Hohenzollern family, and Joachim II (reigned 1535–71), who accepted the Reformation in 1539. In the 17th cent. the electors of Brandenburg acquired (1614) the duchy of Cleves and other W German territories and (1618) the duchy of Prussia (roughly, the later East Prussia). Although it suffered heavily in the Thirty Years War (1618–48), Brandenburg emerged as a military power under Frederick William, the Great Elector (reigned 1640–88), who acquired E Pomerania and freed Prussia from Polish suzerainty. His son, Elector Frederick III, in 1701 took the title "king in Prussia" as Frederick I. The later history of Brandenburg is that of Prussia.