Opposed to historical oppression's initiator or starter (9)
I believe the answer is:
antipasto
'starter' is the definition.
(I've seen this before)
'opposed to historical oppression's initiator' is the wordplay.
'opposed to' becomes 'anti' (anti means opposing something).
'historical' becomes 'past' (similar in meaning).
'initiator' indicates taking the first letters (I've seen 'initiators' mean this).
The first letter of 'oppressions' is 'o'.
'anti'+'past'+'o'='ANTIPASTO'
'or' acts as a link.
(Other definitions for antipasto that I've seen before include "what to eat first" , "Appetizer course in an Italian meal" , "course leader" , "Italian appetiser" , "first course" .)