Chomsky condemned the US ground invasion and carpet bombing of Kampuchea, which destabilized the country and I'm guessing the mass death of civilians from does not fit into your genocide definition.

In 1975 the coalition led, nominally or not, by Sihanouk gained control of Kampuchea (again, in the case of Sihanouk). The US and west said a genocide was happening between 1975 and 1979, but immediately somewhat covertly, and then openly, began arming the coalition with Pol Pot and what the west called the Khmer Rouge.