The Frisian-Drenthe war was an assault by a Frisian army under the command of the bishop Wilbrand of Oldenburg on the province of Drenthe which lasted from 1231 until 1233.
On 28 July 1227 Bishop Otto II was killed together with many of his knights in the Battle of Ane in the province of Drenthe. Otto’s successor, Wilbrand of Oldenburg, called on the Frisian people to support him in suppressing the rebellious Drenths.
In 1231, Wilbrand invaded Drenthe. The unknown chronicler of Quedam Narracio (an ancient manuscript with tales of Groningen, Drenthe and Coevorden) emphasized that the Frisians aided Wilbrand of their own free will. So many volunteers showed up that the invading army had to be split up into two parts.
The war was not successful. The Frisian army was deceived and betrayed, and lost 50 soldiers while many others were captured by the Drenths. A monastery was established near Marienberg to save the souls of the killed Frisian soldiers.