Use the library catalog WorldCat Discovery to find scholarly books and articles, as well as government publications and other items.
In most cases, it's useful to begin a catalog search with a simple keyword phrase such as:
The library catalog also uses subject headings, which are classification terms for particular topics. You can find relevant subject headings by clicking on the Description of a book. If you know the name of a subject heading, you can also do a search for it in the search box.
For your project, you may find the following subject headings useful:
Central America—Foreign relations—United States
Central America—Politics and government—1979-
Civil Rights—Central America—History—20th Century
Human Rights—Central America—History—20th Century
United States—Foreign relations—Central America
United States—Foreign Relations—Sources
Violence—Central America—History—20th Century