We don't have a whole book on the history of the pledge of allegiance in either print or electronic format.
So, I'm not sure if by book you mean "a source that is not a website I found with Google" or you mean "my professor requires me to use a book for this assignment."
We do have some quality resources in electronic format that look like they will address the history & some of the controversy of the pledge of allegiance. They are in the form of academic journals delivered in electronic format.
Follow this URL, login, and see if any of these might work - https://akin.css.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=aph&bquery=%22pledge+of+allegiance%22&type=0&site=ehost-live
This is a print book. We could try to borrow it for you from another library, but it would take at least a week to get it to you.
| Author |  Ellis, Richard (Richard J.) |
| Title | To the flag : the unlikely history of the Pledge of Allegiance / Richard J. Ellis. |
| Portion of Title | History of the Pledge of Allegiance |
| Publisher |
Lawrence : University Press of Kansas, c2005.
Good luck with your class. |