Heathen commander invading borders of Pakistan (5)
I believe the answer is:
pagan
'heathen' is the definition.
('pagan' can be a synonym of 'heathen')
'commander invading borders of pakistan' is the wordplay.
'commander' becomes 'aga' (I've seen this before).
'invading' is an insertion indicator.
'borders of' means to remove the middle letters.
'pakistan' with its middle removed is 'pn'.
'aga' going within 'pn' is 'PAGAN'.
(Other definitions for pagan that I've seen before include "One who does not acknowledge your god(s)" , "Unbeliever" , "One who follows a polytheistic or pre-Christian religion, but not a Jew" , "One who does not acknowledge a god" , "A heathen, not a Christian" .)