Search for Books
Use the main LibrarySearch to find books on your topic.
Try an simple search for your terms, like renaissance warfare, then limit to "Books" under "Resource Type" on the left hand side:
Then, check the record of a book to find the correct Subjects, and use those to search for more books:
Search I-Share
It's often a good idea to start a search for books with the I-Share catalog. I-Share searches university libraries across Illinois, and will find what we have at DePaul as well as what you can easily request from other libraries.