Query: Harff and Gurr's definition of genocide included the promotion and execution of what, by a state or its agents?
Context: Barbara Harff and Ted Gurr defined genocide as "the promotion and execution of policies by a state or its agents which result in the deaths of a substantial portion of a group ... [when] the victimized groups are defined primarily in terms of their communal characteristics, i.e., ethnicity, religion or nationality."