Not damaged by popular diplomacy (6)
I believe the answer is:
intact
'not damaged' is the definition.
(I've seen this before)
'by popular diplomacy' is the wordplay.
'by' says to put letters next to each other.
'popular' becomes 'in'.
'diplomacy' becomes 'tact' (I've seen this before).
'in' next to 'tact' is 'INTACT'.
(Other definitions for intact that I've seen before include "Complete - unbroken" , "Unbroken and unimpaired" , "Not damaged in any way" , "Undamaged, unimpaired" , "Undamaged, not broken" .)