Make poor group of African warriors keep quiet about past (10)
I believe the answer is:
impoverish
'make poor' is the definition.
(synonyms)
'group of african warriors keep quiet about past' is the wordplay.
'group of african warriors' becomes 'impi' (I've seen this in another clue).
'keep quiet' becomes 'sh' (as in shushing someone).
'about' indicates putting letters inside.
'past' becomes 'over' (both can mean finished).
'impi'+'sh'='impish'
'impish' enclosing 'over' is 'IMPOVERISH'.
(Other definitions for impoverish that I've seen before include "beggar" , "Spoil the quality of" , "Make poor" .)