Dispatched soldiers will invade it — that's the feeling (9)
I believe the answer is:
sentiment
'the feeling' is the definition.
(a sentiment is a feeling or view)
'dispatched soldiers will invade it' is the wordplay.
'dispatched' becomes 'sent' (I've seen this before).
'soldiers' becomes 'men' (men can mean a group of soldiers).
'will invade' means one lot of letters goes inside another.
'men' going within 'it' is 'iment'.
'sent'+'iment'='SENTIMENT'
'that's' acts as a link.
(Other definitions for sentiment that I've seen before include "View, opinion, feeling" , "Tender feeling" , "Emotion, self-indulgent or insincere perhaps" , "Emotional feeling" , "Test men in, say, emotion" .)