Nor historic rivalries not China is the reason.. Afghan cultural fabric is broken,People dont have work those dont want to do petty jobs and earn fast money grow and trade drugs regardless of any ethnicity. Others become guns for hire and become contract killers .many group up to raise militia.The drug dealers have a strong nexus with the terorriist/militias as one finances while other provides security. These groups take orders from outside world as well many knowingly and others unknowingly play in hands of different security agencies from around the world..Though Pakistan and AhmedShah Masoud(Tajik)developed distrust in early 90s but regardless of that these people would do anythign for money so who ever pays a bigger cheque wins their services. Apart from poverty another major problem in Afghan society is child abuse.The problem is at an alarming level and the militias keep hoards of young boys raised for years used in every worse way, that make broken minds brainwashed to become fidaeen.and then they are sent over across the border for their kamikaze missions.Pkaistan is ont he receiving and not Iran or CAR states because of the heavy indian influence and connection with the Afghan govt. and other agencies who do their work in layers.