Great to keep remaining Northern soldiers in control (10)
I believe the answer is:
government
'control' is the definition.
(government is a kind of control)
'great to keep remaining northern soldiers' is the wordplay.
'great' becomes 'gt' (abbreviation used in place names).
'to keep' is an insertion indicator.
'remaining' becomes 'over' (as in 'we ate them all but had one over').
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'soldiers' becomes 'men' (I've seen this before).
'over'+'n'+'men'='overnmen'
'gt' placed around 'overnmen' is 'GOVERNMENT'.
'in' acts as a link.
(Other definitions for government that I've seen before include "Body of rulers" , "A country's rulers" , "Ventnor gem (anag.)" .)