Soldiers only destroyed trust (4,2)
I believe the answer is:
rely on
'trust' is the definition.
(relying on is a kind of trusting)
'soldiers only destroyed' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'destroyed' indicates anagramming the letters.
'only' with letters rearranged gives 'lyon'.
're'+'lyon'='RELY ON'
(Other definitions for rely on that I've seen before include "Trust in with confidence" , "Trust, be confident in" , "Put trust in" .)