 The Dadau has since Reformation Times been marking the border of areas with a predominantly Roman Catholic population from other areas with a predominantly Evangelical, Lutheran population.To the west of this border lay the Niederstift Münster, the Free State of Oldenburg with the region of Oldenburger Münsterland as well as the Regierungsbezirk Weser-Ems in Lower Saxony.To the east of the border is the district of Diepholz, The Kingdom of Hanover, The Kingdom of Prussia as well as the Regierungsbezirk Hannover in Lower Saxony.