Secondary Sources in Literature
These databases are very useful for finding secondary research (criticism and theory) about literature. Search for the title of the book, the author, and/or a keyword phrase such as "early American literature".
Secondary Sources in History
These databases will be useful when searching for secondary research related to the time period or historical movement. JSTOR in particular includes journal issues back to the very first issue (limit your search to the decade(s) after an event happened to see what was written about it at that particular time).