Conscious of fighting in AE (5)
I believe the answer is:
aware
'conscious of' is the definition.
(being conscious means being aware of something)
'fighting in ae' is the wordplay.
'fighting' becomes 'war'.
'in' is an insertion indicator.
'war' inserted into 'ae' is 'AWARE'.
(Other definitions for aware that I've seen before include "Having knowledge or realisation" , "Conscious or having knowledge of" , "Cognisant, mindful" , "Acquainted with or mindful of" , "Informed; conscious" .)