Strength seen in Crimean War — battling back (5)
I believe the answer is:
brawn
'strength' is the definition.
(brawn is a kind of strength)
'in crimean war battling back' is the wordplay.
'in' indicates a hidden word.
'back' is a reversal indicator.
'nwarb' is hidden within 'crimean war battling'.
'nwarb' backwards is 'BRAWN'.
'seen' is the link.
(Other definitions for brawn that I've seen before include "Pressed cooked meat; strength" , "This is strong" , "Physical strength; cooked meat" , "Jellied meat - muscle" , "Jellied meat -- not brain!" .)