Rising American prosecutor joining northern state (5)
I believe the answer is:
sudan
'state' is the definition.
(Sudan is an example)
'rising american prosecutor joining northern' is the wordplay.
'rising' says the letters should be written in reverse (going up in a down clue).
'american' becomes 'us' (abbreviation for United States).
'prosecutor' becomes 'da' (D.A. is an example).
'joining' is a charade indicator (letters next to each other).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'us' written backwards gives 'su'.
'su'+'da'+'n'='SUDAN'
(Other definitions for sudan that I've seen before include "Home for many Arabs" , "Country between Egypt and Zaire" , "Country W. of Ethiopia" , "Country bordering the Red Sea" , "African country on the Red Sea" .)