Non-belligerent condition is enshrined in treaty (8)
I believe the answer is:
pacifist
'non-belligerent' is the definition.
(I've seen this before)
'condition is enshrined in treaty' is the wordplay.
'condition' becomes 'if' (I've seen this in other clues).
'enshrined in' is an insertion indicator.
'treaty' becomes 'pact' ('pact' can be a synonym of 'treaty').
'if'+'is'='ifis'
'ifis' going into 'pact' is 'PACIFIST'.
(Other definitions for pacifist that I've seen before include "War opponent" , "non-belligerent" , "Person opposed to war" , "Someone believing all war is wrong" , "Person who believes in resolving quarrels by peaceful means" .)