The guys above faced all the dangers. Not the likes of Ibrahim Ali, Nazri Aziz or those PSM guys. Mass killings occurred under some Communist regimes during the twentieth century with an estimated death toll numbering between 85 and 100 million.^[1] Scholarship focuses on the causes of mass killings in single societies, though some claims of common causes for mass killings have been made. Some higher estimates of mass killings include not only mass murders or executions that took place during the elimination of political opponents, civil wars, terror campaigns, and land reforms, but also lives lost due to war, famine, disease, and exhaustion in labor camps.

There are scholars who believe that government policies and mistakes in management contributed to these calamities, and, based on that conclusion combine all these deaths under the categories "mass killings", democide, politicide, "classicide", or loosely defined genocide. According to these scholars, the total death toll of the mass killings defined in this way amounts to many tens of millions; however, the validity of this approach is questioned by other scholars. As of 2011, academic consensus has not been achieved on causes of large scale killings by states, including by states governed by communists. In particular, the number of comparative studies suggesting causes is limited.

The highest death tolls that have been documented in communist states occurred in the Soviet Union under Joseph Stalin, in the People's Republic of China under Mao Zedong, and in Cambodia under the Khmer Rouge. The estimates of the number of non-combatants killed by these three regimes alone range from a low of 21 million to a high of 70 million.^{[2][dubious – discuss]} There have also been killings on a smaller scale in North Korea, Vietnam, and some Eastern European and African countries.