As you saw before the library offers several search systems that you can use to find publications. The search techniques in these catalogues, databases and search engines are not the same.
When you choose for a catalogue or database with controlled vocabulary you have to 'translate' the elements of your topic in the terminology that the database uses.
When you are searching in a database or search engine without controlled vocabulary you have to formulate your searches with the keywords you found during the orientation phase.
All the elements of your topic have to be covered by keywords and their synonyms.
As we indicated before SmartCat has its limitations when you want to search with controlled vocabulary, but you can search SmartCat with keywords.
If your search produces too many results, you need to make your search more specific.
Perhaps you use the search term WAR, while you only want information about CIVIL WAR.
When your research question is focused on a specific aspect of civil war you can add this element to your search.
If your search produces too few results, you need to broaden your search terms or add synonyms.