As mentioned previously, "When Wizard Stay Up Late - The Origins of the Internet" is considered by many as the authoritative text on how the Internet came to be.

For more technical aspects and if you're inclined to sift through tons of emails, mailing lists archives may be of interest

for example the end-to-end mailing list http://www.postel.org/e2e.html (seems down at the moment)

also various IETF mailing lists archives - https://datatracker.ietf.org/list/wg/