Hmm lemmesee, Russia invaded and left, America and Britain(Tony Blair) invaded and will leave at some point.
Now, what other regional powers have borders with Afghanistan and fancy their chances?
The Afghans will quite happily fight any incomers and sticking a name like Taliban on them doesnt change their nationality. They've done it for millenia. They were doing it when Alexander the Great wandered through.
http://www.afghanland.com/history/alexander.html
http://en.wikipedia.org/wiki/First_Anglo-Afghan_War
http://en.wikipedia.org/wiki/Second_Anglo-Afghan_War
http://en.wikipedia.org/wiki/Third_Afghan_War