Check my term paper on the prohibition of marijuana here:

http://boards.cannabis.com/showthread.php?t=37653

Two books to read are:

Jack Herer's "The Emperor Wears No Clothes", which is clear, concise, and fascinating.

Larry Sloman's "Reefer Madness"-- a 300 page social history of marijuana in America-- one of the best non-fiction books I've ever read, but it may not be so helpful if the paper's due in a week.