The state of Prussia had its origins in the separate lands of the Margraviate of Brandenburg and the Duchy of Prussia. The Margraviate of Brandenburg developed from the medieval Northern March of the Holy Roman Empire, passing to the House of Hohenzollern in 1415. The Duchy of Prussia was created in 1525 when the eastern lands of the Teutonic Knights were secularized as Polish fief by Albert of Brandenburg-Ansbach, a member of a cadet branch of the Hohenzollerns. Prince-elector George William inherited the Duchy of Prussia in 1618, uniting Brandenburg and Prussia under one ruler; the elector's state became known as Brandenburg-Prussia. The Kingdom of Prussia was created when Elector Frederick III assumed the title of Frederick I, King in Prussia, on 18 January 1701.
Prussia ceased to be a kingdom after the fall of the German Empire resulting from World War I, becoming instead the Free State of Prussia. The state of Prussia was abolished in 1947 following World War II.