States in America against leaving US (5)
I believe the answer is:
avers
'states in' is the definition.
'avers' can be an answer for 'states' (to aver is to declare or state). I am unsure of the 'in' bit.
'america against leaving us' is the wordplay.
'america' becomes 'A' (common abbreviation eg in USA).
'against' means one lot of letters go next to another.
'leaving us' becomes 'vers' (I can't justify this - if you can you should believe this answer much more).
'a'+'vers'='AVERS'
Can you help me to learn more?
(Other definitions for avers that I've seen before include "Swears" , "Alleges, asserts" , "States positively" , "Declares to be true" , "States firmly - really raves" .)