Tribalists' centre in Indonesia (4)
I believe the answer is:
bali
'in indonesia' is the definition.
('Bali' is part of 'indonesia')
'tribalists' centre' is the wordplay.
'centre' says to take the centre.
The middle of 'tribalists' is 'BALI'.
(Other definitions for bali that I've seen before include "Bail out of the island" , "Middle East country" , "mountainous island" , "Island in Indonesia" , "Indonesian island, capital Denpasar" .)