Modern nation on threat of revolutionary (5-2-3-3)
I believe the answer is:
state-of-the-art
'modern' is the definition.
('state-of-the-art' can be similar in meaning to 'modern')
'nation on threat of revolutionary' is the subsidiary indication.
'nation' becomes 'state' ('state' can be a synonym of 'nation'**).
'on' is a charade indicator (letters next to each other).
'revolutionary' indicates anagramming the letters.
'threat'+'of'='threatof'
'threatof' anagrammed gives 'oftheart'.
'state'+'oftheart'='stateoftheart'
(Other definitions for state-of-the-art that I've seen before include "Latest and best" , "Incorporating the newest ideas and features" , "Incorporating the latest technologies" , "Modern" , "Up-to-date technically" .)