since the advent of islam in central asia, several types of empires ruled on the region; the arabs empire (umayyads and abbasids), the ghaznavid, the seljuks, the mongols, the tatars, and the russians. the abbasids actual power did not last more than a century and a half and gradually independent states emerged at the eastern parts of the empire. the role of caliphate system was then limited an...