Half of research is knowing how to find it! The following are subject headings related to your topic. You can use the suggested terms below for subject searches in sources like the catalog and Discovery. This is not an inclusive list, but rather some examples of the standardized language used by scholars!
Cities and Towns--Europe--History
Berlin (Germany)--Politics and Government
Sarajevo (Bosnia and Herzegovina)--Social Life and Customs
Narrowing Searches to Date Published/Subject Time Period:
You may have to be strategic about how you search for certain data. For example, searching for simply class structure of x city will probably not get you too far. You might want to get more specific (e.g. unemployment rate x-city 1950 or income demographics x-city 2017). Likewise, you might want to search for x city timeline or history of x city rather than major events in x city (which will probably give you a nice current city calendar, but not probably what you're looking for)! Remember to evaluate your sources for credibility!
Be cautious with Wikipedia sources! These mainly serve the purpose of introducing you to specific examples that you can then verify using the References section of the page or find more information about elsewhere on the web.