Threaten conflict to the north (4)
I believe the answer is:
warn
'threaten' is the definition.
(I know this)
'conflict to the north' is the wordplay.
'conflict' becomes 'war' (war is a kind of conflict).
'to the north' becomes 'N' (abbreviation).
'war'+'n'='WARN'
(Other definitions for warn that I've seen before include "Notify in advance of danger" , "Alert" , "Sound the alarm" , "Notify of potential risk" , "Make aware of danger" .)