Well, when it comes to Marxist atrocities,
the Kmer Rouge indeed hold the Post WW2 record. However, in terms of numbers killed, North Korea is ahead, since it had more people to begin with. Plus, in North Korea, masses of people are not being shot or clubbed to death and buried in mass graves. Instead they are quietly starving to death in the comfort of their homes. In Zimbabwe, the people can't even starve in their homes, because these homes are being demolished by the government. They will have to move back into the wilderness areas to starve. In either case, the people will starve while the leaders get richer and fatter.