If you want to browse the shelves without looking for a particular work, you may wish to consult the Library of Congress Classification Outline. For the purposes of this class, you will find much useful materials in Class P, on the 4th floor of Cabell. All 20th century U.S. fiction can be found in PS, with individual authors and their works, criticism, biographies, etc. in PS3500-PS3549 (1900-1960) or PS3550-3576 (1960-2000). Note, however, that many titles may appear in Class E-F - History of the Americas.
Useful subject headings may include:
[SUBJECT] in literature
[AUTHOR] -- History and criticism
American fiction -- 20th century
American fiction -- 20th century -- History and criticism
Emigration and immigration in literature
Ethnic groups in literature
Ethnicity in literature
Fiction -- History and criticism
Immigrants in literature
Literature and society
Literature and society -- United States
Politics and literature
Politics and literature -- United States
Race in literature
These subject headings will also be useful in WorldCat or other databases that use the Library of Congress' classification system.
These are a sampling of the books in the reference section on the first floor of Cabell Library that might be useful for you in exploring your topic. Each volume contains information about major American authors, literary movements, etc., along with supplementary bibliography that may prove useful in further exploring your topic.
Note: as with the databases, reference works on subjects often treat fiction/novels associated with that subject. E.g. Encyclopedia of the Jazz Age (Cabell Library Reference E784 .E53 2007).
If you can't find the book that you want at VCU, try these resources to find what you need.