River, western Germany.
An important tributary of the lower Rhine River , it rises on the northern side of Winterberg and flows 146 mi (235 km) west. The Ruhr valley is a major industrial and mining region; it includes the industrial cities of Essen , Düsseldorf , and Dortmund . The Ruhr coalfield is one of the world's largest and produces the bulk of Germany's bituminous coal. Industries begun by the Krupp and Thyssen families flourished in the 19th20th centuries (see Thyssen-Krupp Stahl). The river was militarily important in World War I, and the river valley was occupied from 1923 to 1925 by France and Belgium (see Ruhr occupation ). As the industrial heart of Nazi Germany, it was heavily bombed in World War II and occupied by Allied troops in 1945; full control was returned to West Germany in 1954. It is now a centre of steel production and diversified chemical manufacturing.