Region united behind leader of Zulus (4)
I believe the answer is:
zone
'region' is the definition.
(I know that zone is a type of region)
'united behind leader of zulus' is the wordplay.
'united' becomes 'one' (as in a phrase like 'we are one').
'behind' is a charade indicator (letters next to each other).
'leader of' suggests taking the first letters.
The first letter of 'zulus' is 'z'.
'one' put after 'z' is 'ZONE'.
(Other definitions for zone that I've seen before include "Marked area" , "Area, division" , "Particular area or sector" , "Region; time area" , "Area with a particular characteristic" .)