Here is a reference to a dense article from The Claremont Institute by Stanley Kurtz looking at the work of Akbar S. Ahmed who was once governor of the Waziristan region of Pakistan. Essentially, it looks at the tribal ethos and the way it interacts with militant Islam. The article itself is interesting, particularly for foreign policy wonks.
One thing the article suggests to me is that the Pushtun tribes in Waziristan behave in ways similar to the violent youth gangs of our U.S. inner cities. The tribal emphasis on collective guilt, honor, humiliation and revenge is very like what plays out on our mean streets. Perhaps this is what humans do in the absence of law and order?