sentences:  With the abdication of King John II Casimir of Poland as the last Duke of Opole in 1668, the region passed to the direct control of the Habsburgs.At the beginning of the 18th century the German population of Opole was estimated at around 20%.King Frederick II of Prussia conquered most of Silesia from Austria in 1740 during the Silesian Wars; Prussian control was confirmed in the Peace of Breslau in 1742.