Domain of politician in Ireland (6)
I believe the answer is:
empire
'domain' is the definition.
(I know that empire is a type of domain)
'politician in ireland' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'in' indicates putting letters inside.
'ireland' becomes 'eire' (poetic name for Ireland).
'mp' going into 'eire' is 'EMPIRE'.
'of' is the link.
(Other definitions for empire that I've seen before include "Sovereign state" , "Huge domain or group of companies" , "Eg Holy Roman, British or Ottoman" , "Of furniture and dress style of Napoleon I period" , "Group of states with a single monarch" .)