Book published that is about sultanate (6)
I believe the answer is:
brunei
'sultanate' is the definition.
(Brunei is an example)
'book published that is about' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'published' becomes 'run' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'about' is a reversal indicator.
'ie' in reverse letter order is 'ei'.
'b'+'run'+'ei'='BRUNEI'
Can you help me to learn more?
(Other definitions for brunei that I've seen before include "Its sultan is famously very wealthy" , "Commonwealth member" , "Far Eastern sultanate" , "Southeast Asian sultanate" , "North Borneo sultanate" .)