Ancient kingdom amid ocean that's stormy (9)
I believe the answer is:
macedonia
'ancient kingdom' is the definition.
'amid ocean that's stormy' is the wordplay.
'that's stormy' is an anagram indicator.
'amid'+'ocean'='amidocean'
'amidocean' is an anagram of 'MACEDONIA'.
(Other definitions for macedonia that I've seen before include "Alexander the Great's homeland" , "European country, capital Skopje" , "Landlocked Balkan country" , "Southeast European country" , "republic" .)