Armed forces (6)
'armed forces' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for troops that I've seen before include "Military forces" , "Soldiers, armed forces" , "Military divisions" , "Cavalry" , "Groups of soldiers" .)
(Other definitions for militia that I've seen before include "Reservists" , "Fighting force of civilians" , "Citizen army" , "Body of civilian soldiers" , "Civilian soldier force" .)