Leave American Indian territory (3)
I believe the answer is:
goa
'indian territory' is the definition.
(I've seen this before)
'leave american' is the wordplay.
'leave' becomes 'go'.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'go'+'a'='GOA'
(Other definitions for goa that I've seen before include "State on west coast of India" , "Indian state, formerly Portuguese" , "gazelle?" , "State of India, a former Portuguese colony" , "Indian port" .)