Rebel creating revolutionary stir in countries (15)
I believe the answer is:
insurrectionist
'rebel' is the definition.
('insurrectionist' can be a synonym of 'rebel')
'revolutionary stir in countries' is the wordplay.
'revolutionary' indicates an anagram.
'stir'+'in'+'countries'='stirincountries'
'stirincountries' anagrammed gives 'INSURRECTIONIST'.
'creating' acts as a link.
(Other definitions for insurrectionist that I've seen before include "Revolting type" , "One giving revolutionary" .)