Resumption of harmonious relations (13)
I believe the answer is:
rapprochement
'resumption of harmonious relations' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rapprochement that I've seen before include "resumption of friendly relations" , "Resumption of harmonious relations" , "Re-establishment of harmonious relations" , "Renewal of cordial relations" , "move towards peace?" .)