Why was the decision not to abolish the caliphate was a shrewd one? Describe. 

The decision not to abolish the caliphate was a shrewd one, because another Shiite dynasty, the Fatimids, had ambitions to rule the Islamic world.
The Fatimids belonged to the Ismaili sub-sect of Shiism and claimed to be descended from the Prophet’s daughter, Fatima, and hence, the sole rightful rulers of Islam. From their base in North Africa, they conquered Egypt in 969 and established the Fatimid caliphate. The old capital of Egypt, Fustat, was replaced by a new city, Qahira (Cairo), founded on the day of the rise of the planet Mars (Mirrikh, also called al-Qahir). The two rival dynasties patronised Shiite administrators, poets and scholars.