The same chief for the region (6)
I believe the answer is:
domain
'the region' is the definition.
(domain is a kind of region)
'the same chief' is the wordplay.
'the same' becomes 'do' (abbreviation for ditto).
'chief' becomes 'main' (I've seen this before).
'do'+'main'='DOMAIN'
'for' is the link.
(Other definitions for domain that I've seen before include "Sphere or territory" , "District or area - or range of influence" , "estate" , "Range of influence or field of activity" , "Sphere of activity" .)