Stop white ant engulfing North America (9)
I believe the answer is:
terminate
'stop' is the definition.
('terminate' can be a synonym of 'stop')
'white ant engulfing north america' is the wordplay.
'white ant' becomes 'termite' ('termite' can be a synonym of 'white ant').
'engulfing' means one lot of letters goes inside another.
'north america' becomes 'na'.
'termite' going around 'na' is 'TERMINATE'.
(Other definitions for terminate that I've seen before include "Stop" , "Kill off" , "Put an end to, finish" , "Finalise" , "Cut short" .)