"One Tribe at a Time" will eventually become mandatory reading for those following Afghanistan. Over the past several weeks, we have seen excerpts posted on Steven Pressfield's blog. The full paper is now available for download and is easily THE definitive document on tribal engagement.
You can download the PDF here.
Two sources often cited in the paper:
RAND: Counterinsurgency in Afghanistan
and
Koran, Kalashnikov, and Laptop: The Neo-Taliban Insurgency in Afghanistan 2002-2007 by Antonio Giustozzi