Use encyclopedia articles to learn more about your topic. Ask:
Who cares about my topic? (specific philosophers, rulers or peoples)
What are they arguing about in my topic? What are the controversies?
Are there specific events related to my topic or specific theories or writings?
Here is an example. First, I searched the Oxford Encyclopedia and learned that Pliny wrote about eclipses.
Then, I searched those keywords in Gale:
I can use the bibliographies I find, but I can also mine the articles for more keywords. He seemed to associate the moon with femininity and thought that if a woman's menses coincided with an eclipse, something catastrophic would happen.