Answer by soldiers must be commitment
I believe the answer is:
resolution
'commitment' is the definition.
(thesaurus)
'answer by soldiers' is the wordplay.
'answer' becomes 'solution' ('solution' can be a synonym of 'answer'**).
'by' means one lot of letters go next to another.
'soldiers' becomes 're' (Royal Engineers).
'solution' after 're' is 'RESOLUTION'.
'must be' is the link.
(Other definitions for resolution that I've seen before include "Fixed determination" , "purpose" , "Timely statement of intent" , "Firmness - outcome of decision making" , "puts an end to discord" .)