In camp, no politician was a ruler! (4)
I believe the answer is:
inca
'a ruler' is the definition.
(I know that Inca is a type of queen)
'in camp no politician' is the wordplay.
'no' suggests deleting specific letters.
'politician' becomes 'pm' (short for prime minister).
'camp' with 'pm' taken out is 'ca'.
'in'+'ca'='INCA'
'was' acts as a link.
(Other definitions for inca that I've seen before include "Member of old Peruvian Indian race" , "Ancient Peruvian like Cain" , "Language" , "Old Peruvian descended from Cain" , "Member of Andean people conquered by Spain" .)