Domain of Delaware Nation (5)
I believe the answer is:
arena
'domain' is the definition.
(I know that domain can be written as arena)
'of delaware nation' is the wordplay.
'of' indicates the answer is hidden within the clue.
'ARENA' is hidden in the letters of 'delaware nation'.
(Other definitions for arena that I've seen before include "park" , "Enclosure for sports etc." , "Area of endeavour" , "Ring for contest" , "Ring; stadium" .)