Most powerful elite guards in conflict retreated (9)

'most powerful' is the definition.
('brawny' can be a synonym of 'powerful')

'elite guards in conflict retreated' is the wordplay.
'elite' becomes 'best' (I've seen this in another clue).
'guards' means one lot of letters goes inside another (inserted letters are guarded).
'conflict' becomes 'war' (war is a kind of conflict).
'retreated' says the letters should be written in reverse (I've seen 'retreat' mean this).
'in'+'war'='inwar'
'inwar' backwards is 'rawni'.
'best' going around 'rawni' is 'BRAWNIEST'.