This paper will discuss the reasons for the break-up of the Abbasid caliphate in the ninth and early tenth century CE. It will argue that there were severe cyclical economic problems, exacerbated by political instability. These led to the collapse of the agricultural systems of greater Mesopotamia whose resources had sustained the imperial structures. The economic problems had been made worse by the increasing remoteness of the governing elite, largely of Easter Iranian and Central Asian origin, from the wider Muslim community which undermined residual popular loyalties to the caliphate. This in turn led to the emergence of new regional powers, Muslim but seperatist which pointed the way to the emergence of the post-imperial Muslim Commonwealth.