A question that recurs in genocide studies is whether or not the crimes of Stalin and Mao can be classed as genocides. In the strictest sense, it would be difficult to justify such a classification, because the millions of victims murdered by these regimes were chosen on political and economic grounds, not ethnic or racial in most cases. However, a continuity between these killings and genocide can be found in the theme of pollution. I have already applied this concept to the Nazis here and to the Khmer Rouge here.
As Eric Weitz has noted, the revolutionary, utopian nature of Stalinism and Maoism, and their ultimate origins in world wars, made them prone to seek cleansing missions. Whilst such cleansing did not seek partial or total biological extermination in the Nazi sense, it had the potential to be unlimited in its effects, as occurred ultimately with the Khmer Rouge. I would argue that exploring these connections may be more fruitful than confining the field to events that fit a definition of genocide.