Hawk from marines operating in venture (9)
I believe the answer is:
warmonger
'hawk' is the definition.
(hawk can mean someone urging military action)
'marines operating in venture' is the wordplay.
'marines' becomes 'RM' (abbreviation for 'Royal Marines').
'operating' becomes 'on' (I've seen this in other clues).
'in' indicates putting letters inside.
'venture' becomes 'wager' (wager is a kind of venture).
'rm'+'on'='rmon'
'rmon' placed inside 'wager' is 'WARMONGER'.
'from' is the link.
(Other definitions for warmonger that I've seen before include "Aggressor" , "Bellicose type" , "Hitler, perhaps" , "Hawk" , "Jingoistic individual" .)