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Relationship to religion

Democratic Kampuchea was an atheist state, although its constitution stated that everyone had freedom of religion, or not to hold a religion. However, it specified that what it termed "reactionary religion" would not be permitted. While in practice religious activity was not tolerated, the relationship of the CPK to the majority Cambodian Theravada Buddhism was complex; several key figures in its history such as Tou Samouth and Ta Mok were former monks, along with many lower level cadres, who often proved some of the strictest disciplinarians. While there was extreme harassment of Buddhist institutions, there was a tendency for the CPK regime to internalise and reconfigure the symbolism and language of Cambodian Buddhism so that many revolutionary slogans mimicked the formulae learned by young monks during their training. Some cadres who had previously been monks interpreted their change of vocation as a simple movement from a lower to a higher religion, mirroring attitudes around the growth of Cao Dai in the 1920s.

Buddhist laity seem not to have been singled out for persecution, although traditional belief in the tutelary spirits, or neak ta, rapidly eroded as people were forcibly moved from their home areas. The position with Buddhist monks was more complicated: as with Islam, many religious leaders were killed whereas many ordinary monks were sent to remote monasteries where they were subjected to hard physical labour. The same division between rural and urban populations was seen in the regime's treatment of monks. For instance, those from urban monasteries were classified as "new monks" and sent to rural areas to live alongside "base monks" of peasant background, who were classified as "proper and revolutionary". Monks were not ordered to defrock until as late as 1977 in Kratié Province, where many monks found that they reverted to the status of lay peasantry as the agricultural work they were allocated to involved regular breaches of monastic rules. While there is evidence of widespread vandalism of Buddhist monasteries, many more than were initially thought survived the Khmer Rouge years in fair condition, as did most Khmer historical monuments, and it is possible that stories of their near-total destruction were propaganda issued by the successor People's Republic of Kampuchea. Nevertheless, it has been estimated that nearly 25,000 Buddhist monks were killed by the regime.

The repression of Islam (practised by the country's Cham minority) was extensive. Islamic religious leaders were executed, although some Cham Muslims appear to have been told they could continue devotions in private as long as it did not interfere with work quotas. Mat Ly, a Cham who served as the deputy minister of agriculture under the People's Republic of Kampuchea, stated that Khmer Rouge troops had perpetrated a number of massacres in Cham villages in the Central and Eastern zones where the residents had refused to give up Islamic customs. While François Ponchaud stated that Christians were invariably taken away and killed with the accusation of having links with the U.S. Central Intelligence Agency, at least some cadres appear to have regarded it as preferable to the "feudal" class-based Buddhism. Nevertheless, it remained deeply suspect to the regime thanks to its close links to French colonialism; Phnom Penh cathedral was razed along with other places of worship.