Kingdom not fancied by leader of monarchists (5)
I believe the answer is:
realm
'kingdom' is the definition.
(kingdom is a type of country or realm)
'not fancied by leader of monarchists' is the wordplay.
'not fancied' becomes 'real' (I've seen this in other clues).
'by' is a charade indicator (letters next to each other).
'leader of' says to take the initial letters.
The initial letter of 'monarchists' is 'm'.
'real'+'m'='REALM'
(Other definitions for realm that I've seen before include "Area of interest/activity" , "Province" , "Area of knowledge under discussion" , "the UK, perhaps" , "Land under a king or queen" .)