"In the 1970s, the Khmer Rouge were largely supported and funded by the Chinese Communist Party, receiving approval from Mao Zedong; it is estimated that at least 90% of the foreign aid which was provided to the Khmer Rouge came from China."
> In 1970, the United States had orchestrated a coup to oust Prince Sihanouk, and installed Lon Nol, a general who was supposed to be Cambodia’s Suharto. His forces trained in Bandung, not far from the site of Sukarno’s 1955 Afro-Asian Conference. During Lon Nol’s rule the United States continued to bomb the country indiscriminately, killing hundreds of thousands of people, mostly peasants, in a futile attempt to stop Vietnamese communists from moving through the countryside. The United States dropped three times the tonnage on Cambodia that fell on Japan during World War II, atom bombs included.
> [...]
> The disregard for life was staggering, and well understood in Southeast Asia. Traumatized refugees flooded Cambodia’s cities. After the US-backed coup that deposed him, the ousted prince, Sihanouk, published a book of memoirs titled My War with the CIA. “We refused to become US puppets, or join in the anti-communist crusade,” he wrote. “That was our crime.” He threw his support behind the small, shadowy, and strange group of Marxists he had repressed while in power. The Khmer Rouge, as he called them in the old colonial language, were the only ones fighting against Lon Nol and the US Army, which was wiping out entire swathes of the population.
Pol Pot was convinced of the necessity of armed struggle by the annihilation of the PKI in Indonesia. There ~1 million people were killed with the encouragement of the US and Britain, who supplied arms, kill lists, and promises of economic development.
[2]
> In a “historical lessons” document composed in early 1977, Pol Pot looked back on the 1966 period as follows: “If our analysis had failed, we would have been in greater danger than [were the communists] in Indonesia. But our analysis was victorious, because our analysis was agreed upon, because most of our cadres were in life-and-death contradiction with the enemy; the enemy sought to exterminate them constantly.”
After Vietnam invaded Cambodia and put a stop to the Khmer Rouge's Killing Fields:
[3]
> The United States chose to recognize the remnants of the Khmer Rouge at the United Nations, keeping its tiny regime alive, and refusing to recognize the Vietnamese-allied government. This would last for years. Partly, it was a way to appease Carter’s new ally in Beijing. But Benny knew that it was something else too. “They hated Vietnam too much,” Benny said. “They couldn’t forgive them for winning the war.”
[4]
> And to insure that Pol Pot and the Khmer Rouge would fight the Vietnamese occupiers, the Carter Administration helped arrange continued Chinese aid.
> "I encourage the Chinese to support Pol Pot," said Zbigniew Brzezinski, the national security adviser at the time. "The question was how to help the Cambodian people. Pol Pot was an abomination. We could never support him, but China could."
> At the United Nations, the United States, along with most countries of Europe and Asia, gave the Cambodia seat to the Khmer Rouge Government by itself and, after 1983, in coalition with other anti-Vietnamese Cambodian groups.
> All attempts even to describe the Khmer Rouge regime as genocidal were rejected by the United States as counterproductive to finding peace. Only in 1989, with the beginning of the Paris peace process, was the word genocide spoken in reference to a regime responsible for the deaths of more than a million people.
[1][2][3] - The Jakarta Method, chapters 2, 4, and 10 (also contains more detailed sources)
Thanks I hadn't been aware of some of those later points. I found some more referenced in another article[1]. I'll try read the full NY Times link but reached limit of my free access for the month.
"In the 1970s, the Khmer Rouge were largely supported and funded by the Chinese Communist Party, receiving approval from Mao Zedong; it is estimated that at least 90% of the foreign aid which was provided to the Khmer Rouge came from China."
https://en.m.wikipedia.org/wiki/Khmer_Rouge