American behind position supporting international aid (10)
I believe the answer is:
assistance
'aid' is the definition.
(assistance is aid or help)
'american behind position supporting international' is the wordplay.
'american behind' becomes 'ass' (primarily US term for one's behind).
'position' becomes 'stance' (stance is a kind of position).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'international' becomes 'i' (abbreviation eg in IMF).
'stance' put after 'i' is 'istance'.
'ass'+'istance'='ASSISTANCE'
(Other definitions for assistance that I've seen before include "Support" , "Aid" , "Help" .)