Group of states nourished with vitamin allowance (10)
I believe the answer is:
federation
'group of states' is the definition.
(I've seen this before)
'nourished with vitamin allowance' is the wordplay.
'nourished' becomes 'fed' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'vitamin' becomes 'E' (E is an example).
'allowance' becomes 'ration' (I've seen this before).
'fed'+'e'+'ration'='FEDERATION'
(Other definitions for federation that I've seen before include "Group of states" , "Russia, for one" , "Alliance" , "Union of states" .)