Peaceful coexistence (7)
(Other definitions for harmony that I've seen before include "Pleasing blend of sounds" , "sounds agreeable" , "Mutual rapport" , "Pleasing combination of musical notes" , "Accord" .)
'peaceful coexistence' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for detente that I've seen before include "Relaxed relations" , "peace during hostilities" , "Slackening of tension" , "Easing of international hostility" , "The easing of tensions between nations" .)