Asian sultanate (6)
I believe the answer is:
brunei
'asian sultanate' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for brunei that I've seen before include "North Borneo sultanate" , "It's sultan is immensely rich" , "Commonwealth member" , "Sultanate on the island of Borneo" , "Commonwealth country" .)