Background or "reference" sources are a great place to start in building your bibliographies. These are scholarly encyclopedias, handbooks, bibliographies, and similar sources that will often contain lengthy essays with background information on a topic and overviews of the relevant scholarship. Citations to the secondary literature will always be included, and often so too will citations to primary sources.
The SHAFR Guide Online: An Annotated Bibliography of U.S. Foreign Relations since 1600
Latest edition of the major reference work for the study of U.S. foreign relations. Includes "The United States and the Vietnam War" (Ch. 17).
A key reference collection. Relevant works here include The Cambridge History of the Cold War and The Cambridge History of Southeast Asia: Volume 2: The Nineteenth and Twentieth Centuries.
Oxford Research Encyclopedia in American History
The articles here are arranged into subfields such as 20th Century: Post-1945, Foreign Relations & Foreign Policy, and Political History. Included are the articles "Origins of the Vietnam War," "American Military Strategy in the Vietnam War, 1965-1973," and more.
This is a large collection of bibliographic “articles,” each containing numerous bibliographic annotations, often of both primary and secondary sources.
Gale Virtual Reference Library
Includes the International Encyclopedia of the Social Sciences and other sources useful for quick references.
This guide is intended for students in Professor David Engerman's course and provides an overview of key resources in the Yale Library for writing your research papers this semester.