The cambodian genocide was carried out by fascists who were supported by the US and shitty Chinese policy. They were crushed by socialist vietnamese soldiers.

Pol pot claimed to be socialist. The nazis called themselves the national socialist party, and we all know based on their record that was a lie, as communists, socialists, and trade unionists were their biggest domestic enemies. Next you'll blame the holocaust on socialists, despite the socialists being in the camps. Don't be so credulous.

Edit: also, the US killed many Cambodians with mass bombings during the same era, which is a fun fact that is relevant given the fascists there were allied with the US government as they carried out their mass killings.