Terrible danger descending on a country (7)
I believe the answer is:
grenada
'country' is the definition.
(I know that Grenada is a country)
'terrible danger descending on a' is the wordplay.
'terrible' indicates anagramming the letters.
'descending on' is a charade indicator (letters next to each other) (in a down clue, some letters go on top of others).
'danger' anagrammed gives 'grenad'.
'grenad'+'a'='GRENADA'
(Other definitions for grenada that I've seen before include "W, Indies island" , "West Indian country" , "Caribbean island country" , "Dare nag go to the West Indies?" , "Island just north of Trinidad" .)