The Rhineland is a region around and south of Cologne, along the river Rhine. The Rhineland became part of Prussia in 1815. After WWI the heavily industrialized region was under the control of French forces until 1930, to form a buffer zone between Germany and France, and remained demilitarized afterwards. Hitler ended its status as demilitarized zone unilaterally in 1936. The Rhineland is part of the modern German states of Rhineland-Palatinate and North Rhine-Westphalia.