When the radical communist Khmer Rouge guerilla conquered Phnom Penh on 17 April 1975, they first restored the old royalist symbols of state and made Prince Sihanouk again head of state. But in 1976, they declared Cambodia the “Democratic Kampuchea”, and adopted its own anthem, in a typical communist style of anthem, commemorating the communist takeover of the capital. Although the text seems to predict the massacres caused by the Khmer Rouge by mentioning “blood” several times in the lyrics, it might also be the case that the lyrics rather took pattern from revolutionary songs in classical Marseillaise style. It has also been suggested that the leader of the Khmer Rouge (and president of the country during this time) Pol Pot may have written this anthem himself.
After the fall of the Khmer Rouge government to Vietnamese forces (who installed a pro-Vietnamese government) the Khmer Rouge continued use of this anthem in exile. Since the Khmer Rouge was recognized as the legitimate government of Cambodia by many Western nations and the United Nations, its anthem continued to be presented as the national anthem of Cambodia in the West until the restoration of the monarchy in 1993.
Special thanks to: Jan Scotland for some of this information.