Opposing appeal North America backs (4)
I believe the answer is:
anti
'opposing' is the definition.
(prefix meaning 'opposing')
'appeal north america backs' is the wordplay.
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'north america' becomes 'na'.
'backs' says the letters should be written backwards.
'it'+'na'='itna'
'itna' back-to-front is 'ANTI'.
(Other definitions for anti that I've seen before include "one opposing?" , "Someone opposed (to a policy?)" , "Prefix meaning against" , "Not favouring" , "Opposed to followers of Hitler" .)