The exclusion of social and political groups as targets of genocide in the CPPCG legal definition has been criticized by some historians and sociologists, for example M. Hassan Kakar in his book The Soviet Invasion and the Afghan Response, 1979–1982 argues that the international definition of genocide is too restricted, and that it should include political groups or any group so defined by the perpetrator and quotes Chalk and Jonassohn: "Genocide is a form of one-sided mass killing in which a state or other authority intends to destroy a group, as that group and membership in it are defined by the perpetrator." While there are various definitions of the term, Adam Jones states that the majority of genocide scholars consider that "intent to destroy" is a requirement for any act to be labelled genocide, and that there is growing agreement on the inclusion of the physical destruction criterion.