Simplify the following text for a Grade 6 native English-speaking person.
Original: Therefore , this constitutes a rare period in history in which the descendants of Ali ( hence the name Fatimid , referring to Ali 's wife Fatima ) and the Caliphate were united to any degree , excepting the final period of the Rashidun Caliphate under Ali himself .
Simplified: ( With the only other exception : the Caliphate of Ali himself . )