An excellent way to discover additional resources is to browse for books in relevant call number ranges.
D501 - D680 - History, General, ... World War I (1914-1918)
DD228.8 - History of Germany, ... Period of World War I, 1914-1918
E766 - E783 - [United States] Wilson's administrations, 1913-1921
E780 - [United States] Internal history during World War I
D720 - D728 - History, General, ... Period between World Wars (1919-1939)
To discover the call number ranges for broader, narrower, or different subjects, consult the Library of Congress Classification Outline.
Subject headings allow you to find books according to broader and narrower topics.
Below are sample subjects. To browse for different, broader, or narrower subjects, go to the library catalog and click "Exact Search." Enter a term and click "subject."
You can start browsing for a broad subject like Education, then look for more specific subjects, such as Education England History 18th century.
Once you know some subject headings, you can also just use them as keywords during an advanced search, using the subject row.