Here is a link showing in chronological order the political and other developments for the city and Duchy of Oldenburg
The following link provides information about historical developments in Germany at any given time.
A good source for local history timelines can be found in village chronicles. These take historical developments of specific areas into account, and let the researcher have a glimpse of ancestors' lives from various points of view. Ortschroniken can usually be retrieved through a mayor's office or historical societies. A Google search may assist with availability.