Asian sultanate (6)
I believe the answer is:
brunei
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">asian sultanate</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)