seventh bullet
sovietwave
Yes, quite a lot of Western Maoists were supportive of "Democratic Kampuchea", partly because the Khmer Rouge were seen as a successful national liberation movement (they beat the imperial powers and their local puppets before the Vietnamese did) and partly because Pol Pot and Co tended to align themselves with China rather than Russia. Most, but not all, of them eventually realised that this was not a good idea.
I'm no fan of the CP(ML) at all, but they were very much larger and much less nuts than the MIM. They were a real thing rather than a couple of strange lads with a typewriter.
They beat them partly because of the vital support given and large gains made by the Vietnamese on Cambodian soil against FANK, if we look at it from 1970-73. The victories were only two weeks apart, but capturing Phnom Penh before the northerners captured Saigon was a source pride for the CPK.
I think westerners (non-Maoists included) also failed to understand the deterioration of relations between the Cambodian and Vietnamese parties, either seeing outward signs of fraternal solidarity (for a time) or viewing it through a crude understanding of Sino-Soviet enmity.