Berg (bĕrk) [key], former duchy, W Germany, along the right bank of the Rhine River between the Ruhr and Sieg rivers. Düsseldorf was its chief city. A county in the 12th cent., Berg passed (1348) to the dukes of Jülich and in 1380 was made a duchy. In 1423 the duchies of Berg and Jülich were united. On the extinction (1511) of the Berg-Jülich line, Berg passed to Duke John III of Cleves (see Cleves, duchy of), whose line died out in 1609, setting off a virulent struggle over succession that contributed to the outbreak of the Thirty Years War (1618–48). In 1614, Berg was awarded to the Palatinate-Neuburg branch of the Bavarian house of Wittelsbach; the award was confirmed in the Treaty of Cleves (1666). Ceded to France in 1806, Berg was raised to a grand duchy by Napoleon I in favor of Joachim Murat. The Congress of Vienna assigned (1815) the duchy to Prussia.