USC has hundreds of reference books in print that provide authoritative background information to help you get started on your research. Here is just a sampling:
Encyclopedia of the United States in the 19th Century 3 vols. (2001)
Women in the American Civil War 2 vols. (2008)
Encyclopedia of the Reconstruction Era 2 vols. (2006)
Encyclopedia of the Gilded Age and Progressive Era 3 vols. (2005)
There are several ways to search for reference/background sources on your topic:
1) In the USC Libraries main search box, conduct a keyword search that includes the type of resource you're looking for:
native americans and bibliography
slavery and encyclopedia
In the results page, select the Location: "Reference".
2) Another option is to search Reference Universe, an online tool that allows you to search for both print and online reference collections.
3) Go to the LA Times Reference Room in Doheny Memorial Library and browse the shelves.