You can use discipline-specific databases -- for history, politics, IR, and particular regions of the world-- to find relevant journal articles on your topics.
Combine key words and phrases
Use an asterisk to truncate terms, e.g., imperial* finds imperialist and imperialism.
It can sometimes help to add the term "sources" to your search to find records that list sources in the the notes field.
If a pdf isn't provided, use the Get it! Cornell link to find the full-text.