Discover sectarian revolts (9)
I believe the answer is:
ascertain
'discover' is the definition.
(ascertaining is a kind of discovering)
'sectarian revolts' is the wordplay.
'revolts' is an anagram indicator.
'sectarian' is an anagram of 'ASCERTAIN'.
(Other definitions for ascertain that I've seen before include "Learn" , "Cartesian (anag)" , "settle" , "Find out by making enquiries in sectarian way" , "Verify" .)