Nation in which Castro battles with CIA (5,4)
I believe the answer is:
costa rica
'nation' is the definition.
(Costa Rica is an example)
'castro battles with cia' is the wordplay.
'battles with' indicates an anagram (I've seen 'battle' mean this (the letters disrupted as if in battle)).
'castro' anagrammed with 'cia' gives 'COSTA RICA'.
'in which' acts as a link.
(Other definitions for costa rica that I've seen before include "A Socratic country in Central America, oddly" , "Central American republic" , "source of coffee" , "place in Central America" , "A Socratic kind of country in S America" .)