Soldiers capturing American base (4)
I believe the answer is:
mean
'base' is the definition.
(I know that base can be written as mean)
'soldiers capturing american' is the wordplay.
'soldiers' becomes 'men' (men can mean a group of soldiers).
'capturing' is an insertion indicator.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'men' placed around 'a' is 'MEAN'.
(Other definitions for mean that I've seen before include "Signify; tight" , "Relating to flowers" , "Common" , "Stand for - penny-pinching" , "Bad-tempered" .)