Perhaps you should try some spelling variations:
population census » population density, population densities
german history » germany history, human history, german historical
census german » century german, versus germany
20th history » 20.2 history, south history, north history
both history » south history, north history, birth history

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: population census german history ((20th history) or (both history)) historiography.~.
• If you are trying to use Boolean operators, they must be ALL CAPS: population census german history ((20th history) OR (both history)) historiography..
• Adding a wildcard symbol may retrieve word variants: population census german history ((20th history) or (both history)) historiography.*.