WorldCat, for books other libraries have and will send here for you via Interlibrary Loan (ILL).
Definitely read the detailed tips on the Find Books page of this guide to most effectively use the catalog, WorldCat, and ILL.
Definitely search both:
America: History & Life or Historical Abstracts (depending on whether your topic deals with the USA/Canada or not) for discovering articles from the greatest number of history journals and for more search tools, including the Historical Period limiter.
JSTOR, for finding articles from those journals for which we have full text available through the JSTOR database.
Definitely do each of these:
Look for the primary sources used and cited by your secondary sources. Mine the bibliographies of relevant books, articles, and dissertations.
Research Guides and General Historical Bibliography
The Creative Guide to Research
ZA 3075 .R69 2000 Ref.
A guide to finding information both in print and available through the World Wide Web.
Student Guide to Research in the Digital Age : How to Locate and Evaluate Information Sources
ZA 3075 .S74 2006 Ref.
Step-by-step introduction to research process, critical evaluation, and specific information sources. Includes consideration of web content from as recently as 2006. A very well-presented blend of detail and introductory overview.
Dictionary of Concepts in History
D13 .R49 1986 Ref.
Identification and discussion "of some of the key concepts of contemporary historical analysis."
The American Historical Association Guide to Historical Literature
Z 6201 .A55 1995 Ref.
A two volume annotated bibliography "of the finest and most useful books and articles available in every field of historical scholarship."
Foreign Relations Bibliographies
Guide to the Diplomatic History of the United States, 1775-1921
by Samuel Flagg Bemis and Grace Gardner Griffin
Z 6465 .U5 B4 Ref.
LC 1.2:D 62 US Documents - Documents Shelves
A chronological guide to published materials about the diplomatic history of the United States from 1775-1921. Published in 1935.
Guide to American Foreign Relations since 1700
Z 6465. U5 G84 1983 Ref.
Edited by Richard Dean Burns and published by The Society for Historians of American Foreign Relations (SHAFR), this is the much modified and updated successor to Bemis and Griffin.
American Foreign Relations since 1600 : A Guide to the Literature. Second edition.
Z 6465 .U5 G84 2003
This SHAFR publication supersedes their 1983 work by Burns, just as that superseded Bemis and Gardner. This one ought to be the first resort, though the earlier titles also have their value.
Foreign Affairs Bibliography
Focused coverage of foreign affairs materials published during very specific time periods. Produced by the Council on Foreign Relations and organized first by geographical areas and then by subtopics. Editions exist for 1919-1932, 1932-1942, 1952-1962, and 1962-1972. Two editions are also on the Loan Shelves.
U.S. Foreign Relations : A Guide to Information Sources.
Z 6465 .U5 P52 Ref.
Volume 6 in the American Government and History Information Guide Series.
This 1980 work offers a detailed bibliography on many different aspects of the practice and practioners of U.S. foreign relations, including primary sources as well as secondary sources.