Republican in denial about Atlantic territory (7)
I believe the answer is:
ireland
'atlantic territory' is the definition.
'Ireland' can be an answer for 'territory' (Ireland is an example). I am not certain of the 'atlantic' bit.
'republican in denial about' is the wordplay.
'republican' becomes 'R' (political abbreviation).
'in' indicates putting letters inside.
'about' indicates an anagram.
'denial' anagrammed gives 'ieland'.
'r' going within 'ieland' is 'IRELAND'.
Can you help me to learn more?
(Other definitions for ireland that I've seen before include "Nation, the Oireachtas its parliament" , "Erin" , "Eire" , "European country" , "British composer" .)