One in flight from warring nations (4)
I believe the answer is:
gnat
'one in flight' is the definition.
'from warring nations' is the wordplay.
'from' indicates the answer is hidden within the clue.
'GNAT' is hidden within 'warring nations'.
(Other definitions for gnat that I've seen before include "Small bloodsucker" , "Sucker (if female)" , "Insect like small mosquito" , "Stinging insect" , "Small fly that bites" .)