Territory on the left, also (4)
I believe the answer is:
land
'territory' is the definition.
(I know that Land is a petty kingdom)
'on the left also' is the wordplay.
'on' says to put letters next to each other.
'the left' becomes 'L' (common abbreviation).
'also' becomes 'and' (both can mean in addition).
'l'+'and' is 'LAND'.
(Other definitions for land that I've seen before include "Alight; country" , "Part of Germany" , "Come down; territory" , "Capture" , "Come down; country" .)