Both of these were published in 1979 and have since been updated. While modern Paganism is only about 100 years old, these books will help to tell you who we are and where we come from. Do not limit yourself to just the modern authors. Books written by the Farrars and Doreen Valiente are used as reference sources by those self-same modern authors. They can be a little hard to find, but are worth the search.
Older materials are worth a look.
Check out Charles Leland's Aradia and Robert Graves The White Goddess . The Golden Bough hold gems of information. When it comes to real History, as in historically accurate, you must go to history books. All that we have comes from archeological and or historical accounts that have come down to us from the past. If we are to give our religion some validity in the eyes of the world we must try and use at least some real information.