So i’m just starting to learn about the Khmer Rouge and my knowledge of their ideology, beliefs, and intent in Cambodia in the late 1960’s-1970’s is limited. My research thus far has mostly been confined to google searches and video interviews from Cambodian citizens who were present during the time that Khmer Rouge held power. Based on the wiki about the Khmer Rouge it says that Cuba was an opponent of the Khmer Rouge and apparently so was the Soviet Union which I found slightly surprising because they are all influenced in some way or another by Marxism- Leninism concepts. I understand that communist concepts are not a one size fits all issue and I’m mostly just curious about the differences in opinion that they have within these shared beliefs/ socioeconomic systems. I am struggling to find anything specifically that details Cuba’s stance against the Khmer Rouge and I was curious if anyone would be able to provide any information about the Cuban opposition to the Khmer Rouge. Thanks in advance for any information that you might share.
"it says that Cuba was an opponent of the Khmer Rouge and apparently so was the Soviet Union which I found slightly surprising because they are all influenced in some way or another by Marxism- Leninism concepts."
There are some big, worldwide-level geopolitical issues here, as well as some regional power politics. If I were to sum up the former, it would be "Sino-Soviet Split".
Basically, after Stalin's death, and noticeably from 1956 when Khrushchev denounced Stalin and his "cult of personality" in the so-called "Secret Speech" given at the 20th Congress of the Communist Party of the Soviet Union. Mao very strongly disagreed with this "revisionism", and caused relations between the People's Republic of China and the USSR to deteriorate (it got so bad that in 1969 there were border skirmishes between the two countries and they were almost at the point of a general war). The PRC (especially under Mao) very much saw itself as a rival leader for the world communist movement, and also as a more genuine supporter of anti-colonialism. A big reason for Richard Nixon's 1972 visit to China and the eventual establishing of bilateral relations between China and the US is that both countries saw the other as a useful counterweight against the Soviets.
How this played out in terms of Cambodia is more or less as follows. The Khmer Rouge had relatively strong links with China, while Vietnam had gravitated towards being more pro-Soviet. The Khmer Rouge, after taking over Cambodia in 1975 and imposing their genocidal regime there, ended up invading southern Vietnam (which until the 18th century had been ethnically Khmer territory), and Vietnam retaliated by invading Cambodia, and supporting a regime to depose and replace the Khmer Rouge (China continued to support the Khmer Rouge and recognized them as the legitimate government of the country; in a twist of Cold War politics, the US did the same as a matter of supporting the PRC and opposing the USSR). Cuba was likewise a Soviet ally, and would generally support the Soviet stance, although I'm not aware of them having specific issues with the Khmer Rouge beyond that. Interestingly, Cuba had tens of thousands of troops at the time in Angola supporting the Peoples Movement for the Liberation of Angola (MPLA, which has actually ruled the country since 1975, although they stopped being Marxist-Leninist in 1991) and were fighting the US-backed UNITA rebels. Interestingly, UNITA was funded by the People's Republic of China before switching to US and South African support.
Another example of how communist states in the 1970s were far from aligned with each other would be Ethiopa and Somalia. By 1977 both were ruled by communist parties, and both even had Soviet advisors in-country. However, Somalia ended up invading Ethiopia in 1977 (starting the Ogaden War) in an attempt to conquer ethnically-Somali parts of the latter country. This led Cuba to send in tens of thousands of troops to support the Ethiopians and their Soviet advisors, while Somalia expelled its Soviet advisors, began taking aid from Egypt, Saudi Arabia and Italy, and by 1981 from the US and China as well. Realpolitik, alliance systems, and a general "the enemy of my enemy is my friend" definitely trumped ideological concerns between states in this period.