If you do not have access to a library, there are two tools on Google that are useful. One is: Google Scholar You can navigate to it from the Google home page. Many of the articles or books cited on the page will not be directly available from the Internet, but some will. These articles may, in turn, have more references in them. You can also mine the text for information – events, movements, people you have not heard of, in order to learn more.
Here is a sample search for "Al Qaeda" on the google scholar page: Search term Al Qaeda
As you continue your search, you will begin to learn which names are most prominent in the field of your interest. The prominence of these names will give you a baseline sense of where to start reading, although not where to stop!