Ethnic persecution (6)
I believe the answer is:
pogrom
'ethnic persecution' is the definition.
(I know that pogrom is a type of ethnic riot)
This is the entire clue.
(Other definitions for pogrom that I've seen before include "An organised massacre of a people" , "Racial massacre" , "Organised massacre of Jews" , "Mass slaughter" , "Organised persecution of an ethnic group" .)