Head of state returned to deal with military action (7)
I believe the answer is:
retreat
'military action' is the definition.
'retreat' can be an answer for 'action' (retreat is a kind of action). I'm unsure of the 'military' bit.
'head of state returned to deal' is the wordplay.
'head of state' becomes 'ER' (abbreviation for Elizabeth Regina).
'returned' says the letters should be written in reverse.
'to deal' becomes 'treat' (I've seen this before).
'er' reversed gives 're'.
're'+'treat'='RETREAT'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for retreat that I've seen before include "It may be secluded" , "unhappy manoeuvre" , "The Priory, say" , "Go back" , "snug" .)