Province of politician in Ireland (6)
I believe the answer is:
empire
'province' is the definition.
(thesaurus)
'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' inserted inside 'eire' is 'EMPIRE'.
'of' is the link.
(Other definitions for empire that I've seen before include "Supreme rule" , "Corporation" , "Group of states under the same sovereign" , "Of furniture and dress style of Napoleon I period" , "Supreme power over many countries" .)