If you take a look at Afghan history, usually they have united to defend against an outside enemy, and as soon as that's accomplished, they turn and start killing each other. This internal instability is a constant invitation to outside forces to come in. I have to think that after the awful years of the Taliban, most Afghans would want to remain at peace, and get the benefits of the new freedom they've found. But I can't be sure that old habits won't reassert themselves.