Background or "reference" sources are a great place to start your research. Reference works include bibliographies, scholarly encyclopedias, dictionaries, handbooks, and other sources that provide overviews of topics and suggestions for further reading.
Includes the Cambridge Histories and Cambridge Companions -- e.g., The Cambridge History of Law in America, 3 vols. (link here goes to vol. 3, "20th Century and After")
An extensive collection of annotated bibliographies often pointing to both primary and secondary sources. Examples of potentially helpful articles include:
"Democratic Citizenship" by Ugur Altundal and Richard Valelly
"Settler Colonialism" by Tate A. LeFevre
Oxford Handbooks Online
Lengthy chapters in the Oxford Handbooks usually provide helpful overviews of scholarly topics and historical literature, along with suggestions for further reading. A number of the handbooks may be helpful depending on your research topic, such as The Oxford Handbook of African American Citizenship, 1865-Present, The Oxford Handbook of American Immigration and Ethnicity, The Oxford Handbook of Gender and Politics.
Oxford Research Encyclopedia of American History
A scholarly encyclopedia of potentially great use in the early stages of your research project. Each article has a discussion of the literature, including primary sources -- often a great starting point for finding more sources.
The following bibliographic databases will be helpful for finding secondary sources, especially scholarly/peer-reviewed journal articles, magazine articles, book reviews, and citations to book chapters and edited collections of books. Please note: the full text of articles will not always be available in these databases. If you see the "YaleLinks" icon instead of a PDF, click on the icon to discover whether we have online access to the article: