Soldiers besieging southern capital retired in shame … (7)
I believe the answer is:
remorse
'shame' is the definition.
(thesaurus)
'soldiers besieging southern capital retired' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'besieging' is an insertion indicator.
'southern' becomes 's' (abbreviation).
'capital' becomes 'rome' (capital of Italy).
'retired' is a reversal indicator.
's'+'rome'='srome'
'srome' reversed gives 'emors'.
're' going around 'emors' is 'REMORSE'.
'in' acts as a link.
(Other definitions for remorse that I've seen before include "Pangs of conscience" , "Guilty conscience" , "Compunction" , "A feeling of deep regret" , "Contrition for wrongdoing" .)