Manage to remain controlling independent country (6)
I believe the answer is:
brunei
'country' is the definition.
(I've seen this before)
'manage to remain controlling independent' is the wordplay.
'manage' becomes 'run' (I've seen this before).
'to remain' becomes 'be' (I've seen this in other clues).
'controlling' means one lot of letters goes inside another.
'independent' becomes 'i'.
'run' placed inside 'be' is 'brune'.
'brune'+'i'='BRUNEI'
(Other definitions for brunei that I've seen before include "Muslim state" , "Southeast Asian sultanate" , "Eastern land" , "Ill" , "Oil-rich country of Southeast Asia" .)