The Emperor Wears No Clothes - Jack Herer.

From the cover, "The authoritative historical record of the cannabis plant, marijuana prohibition, & how hemp can still save the world." Due to the prohibition this book is hard to find. You may not be able obtain it from your local bookstore. It contains documented information about hemp prohibition (not because it's a drug, but because Hearst, Dupont, and many others wanted to make a lot of money at our expense). It's a classic that revolutionalized the hemp movement; the record of the history of hemp, the conspiracy against it, the prohibition of it, and how hemp can save the planet. See also: http://hempnet.com/home.htm and John Carter's Web Page.
ISBN: 1-878124-00-1, HEMP/Queen of Clubs Publishing, 1995 (Tenth Edition).