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
An extensive collection of annotated bibliographies often pointing to both primary and secondary sources. Includes modules in African American Studies, Anthropology, Art History, and Atlantic History and other potentially useful subject areas - e.g., the Literary and Critical Theory module includes the article "Settler Colonialism," Military History module includes "Militarism," Sociology module includes "Empires and Colonialism," etc.
Oxford Handbooks Online
Lengthy chapters in the Oxford Handbooks usually provide helpful overviews of topics and historiography and suggestions for further reading.
Manuscript and print collections
The search portal for finding archival collections at Yale is Archives at Yale.
Archives at Yale allows you to search the finding aids to thousands of archival collections that are held by several special collections units that are part of the Yale Library. Most of Yale’s archival collections are stored off-site and must be requested at least a day in advance. At the present time, a 24-hour advance appointment to visit the special collections reading room is also required so that our special collections repositories can comply with Covid-19 guidelines and protocols. Links to reserve a seat are available on the Guide to Using Special Collections at the Yale University Library.
Just remember, not all archival material available at Yale is in Archives at Yale. If a collection is less than three boxes, there may simply be an Orbis record for it. You can go to the Advanced Search in Orbis and limit the “Location” to a specific special collection, or limit the “Type” to Archives or Manuscripts. Some archival materials might be recently acquired and not in any catalog or database. If you think that is the case, ask a librarian, curator, or archivist for assistance.
The library holds many collections on microfilm that may be useful, depending on your research topic - here are just a few examples:
In general, searching for "Confidential U.S. State Department Central Files" and "National Security Files" in the Title search field in Orbis/Quicksearch will retrieve the wider set of microfilm collections that are available.