United around military leader and single-minded (7)
I believe the answer is:
focused
'single-minded' is the definition.
'united around military leader' is the wordplay.
'united' becomes 'fused' ('fused' can be similar in meaning to 'united').
'around' means one lot of letters goes inside another.
'military leader' becomes 'oc' (abbreviation for Officer Commanding).
'fused' going around 'oc' is 'FOCUSED'.
'and' acts as a link.
(Other definitions for focused that I've seen before include "(Of light) brought to a point" , "not easily diverted" , "Concentrated on - like camera" .)