Reference sources are extremely useful for providing authoritative overviews and background information on a topic. They will give you the terminology and the key names, dates and concepts that can be used when conducting online searches for scholarly articles, books, as well as for searching for primary sources and historical newspapers. Many reference sources also provide extensive bibliographies that list the important and influential scholarship on a given topic.
USC Libraries has several online collections of Reference books (all require login):
USC has hundreds of reference books, most of which are located in Doheny Library's Los Angeles Times Reference Room.
Here is a sampling:
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.