Private collection primarily including the works of such as Balzac (6)
I believe the answer is:
gallic
'of such as balzac' is the definition.
(Gallic means French - Honore de Balzac was French)
'private collection primarily including the works' is the wordplay.
'private' becomes 'GI' (GI can informally mean a US soldier).
'primarily' says to take the initial letters.
'including' is an insertion indicator.
'the works' becomes 'all' ('the works' means everything available).
The first letter of 'collection' is 'c'.
'gi'+'c'='gic'
'gic' enclosing 'all' is 'GALLIC'.
(Other definitions for gallic that I've seen before include "Of the French/France" , "Typically French or of France" , "Characteristic of the French" , "Like certain wars" , "Pertaining to France" .)