Retaliate for destruction of Geneva (6)
I believe the answer is:
avenge
'retaliate for' is the definition.
(to avenge is to retaliate or get revenge for)
'destruction of geneva' is the wordplay.
'destruction of' indicates anagramming the letters.
'geneva' with letters rearranged gives 'AVENGE'.
(Other definitions for avenge that I've seen before include "Gain retribution" , "Carry out retribution" , "Dish out a dose of own medicine" , "Repay (a wrong)" , "Inflict retribution" .)