I think I mentioned this over at Tacitus -- haven't read that Armstrong book but I did recently purchase another one of hers, a biography of Mohammed. I read the intro so far and she seems a little strange to me, but perhaps I'll like the book. "Fragmentation of Afghanistan" is only for the serious Afghanistan junkie, I'd say. It's not an entertaining read. But Rubin is probably one of the two or three most knowledgeable people about the subject, and he incorporates a good deal of social science analysis that you don't get elsewhere. He has some solid information about the various commanders and how they came to power. Actually, I've reread some of that recently as it helped me understand what the Imperial Hubris guy was arguing. I might be putting up some excerpts here, as they are still relevant today.