Realm or dominion (6)
I believe the answer is:
empire
I believe this is a double definition.
'realm' is the first definition.
(I've seen this before)
'dominion' is the second definition.
(I've seen this before)
(Other definitions for empire that I've seen before include "Wide dominion" , "Group of countries ruled by single supreme authority" , "Group of states ruled by one monarch" , "Widespread political or industrial organisation" , "Sovereign state" .)