A plan involving an upset in American territory (6)
I believe the answer is:
panama
'territory' is the definition.
(Panama is an example)
'a plan involving an upset in american' is the wordplay.
'a' becomes 'an'.
'plan' becomes 'map' (plan can mean a map of something).
'involving' is an insertion indicator.
'an upset' is a reversal indicator.
'in american' becomes 'a' (common abbreviation - e.g. in organisation names. I am not sure about the 'in' bit.).
'an' put inside 'map' is 'manap'.
'manap' backwards is 'panam'.
'panam'+'a'='PANAMA'
Can you help me to learn more?
(Other definitions for panama that I've seen before include "What may be seen overhead" , "Central American country" , "Hat; Central Am. canal" , "Criticise" , "Great canal connecting Atlantic and Pacific" .)