Former German state, since 1946 part of Lower Saxony , Germany.
It was held by the counts of Oldenburg from 0441; 1100 until 1667, when it passed to Denmark. In the late 18th century it was ruled by the bishop of Lübeck, who was made duke of Oldenburg by Joseph II , the Holy Roman emperor. It became a grand duchy in the early 19th century and took Prussia's side in the Austro-Prussian War of 1866. It joined the German Empire in 1871. Its last grand duke abdicated in 1918. The 17th-century grand-ducal palace in the city of Oldenburg (pop., 2002 est.: 155,908) is now a state museum of art and culture.