Perhaps you should try some spelling variations:
population trends » population census
german history » germany history, human history, german historical
trends german » lands german, minds german
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 trends german history ((20th history) OR (both history)) historiography.~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "population trends german history ((20th history) OR (both history)) historiography.".
• Adding a wildcard symbol may retrieve word variants: population trends german history ((20th history) OR (both history)) historiography.*.