Books and journal articles make up the core secondary sources you will use for your research.
Scholarly books (or monographs)
When you search for history materials, you are given the option to conduct a "Subject" search. But what are you actually searching through? When books are cataloged by librarians, they are assigned subject headings from a specific and controlled set of terms (often referred to as a vocabulary), with the most common being Library of Congress Subject Headings. If you search using these subject headings, you will receive more specific search results that are directly linked to the search you conducted.
Searching by subject heading can be difficult if you don't know what the exact subject heading is. If you are unsure, it is often best to start with a keyword search, find relevant materials, and see what subject heading(s) have been attached to the item record. You can also search through Library of Congress Subject Headings online.