Reference resources are a great place to begin your research. They can help you define terms as well as to find basic information about a topic, a chronicle of its history, theories, key people and sometimes a bibliography of additional sources.
There are many different types of reference sources, which include dictionaries, encyclopedias, thesauri, bibliographies, handbooks, style manuals to name a few.
Encyclopedia of American History
E174.E53 2003 (Stauffer Library Reference)
Encyclopedia of American Cultural and Intellectual History
E169.1 .E624 2001 (Stauffer Library Reference)
The Greenwood Encyclopedia of Daily Life in America
E169.1 .G7553 2009 (Stauffer Library Reference)
Bibliographies like Oxford Bibliographies offer authoritative research guides helping you to narrow the vast number of citations to the best scholarship on a given topic.
Although there is not a separate guide for American History, there are guides on African American Studies and Atlantic History and articles on the civil rights movement, populist politics, cold war. world economy 1919-1939, and Vietnam War to name a few.