Writer, endlessly narrow-minded, in Korea, for one (9)
I believe the answer is:
peninsula
'korea for one' is the definition.
(korea is a kind of peninsula)
'writer endlessly narrow-minded' is the wordplay.
'writer' becomes 'pen' (I've seen this before).
'endlessly' means to remove the last letter.
'narrow-minded' becomes 'insular' (I've seen this before).
'insular' with its last letter taken off is 'insula'.
'pen'+'insula'='PENINSULA'
'in' acts as a link.
(Other definitions for peninsula that I've seen before include "Piece of land projecting into water" , "War-zone" , "Lower California, say" , "Jutting-out strip of land" , "Scandinavia, perhaps" .)