[chinhodado]

About North Vietnam's support of the Khmer Rouge early on, it's worth viewing things in historical context. During the Cambodian coup of 1970, Vietnamese ethnic was massacred:

> Paranoia flourished and this set off a violent reaction against the nation's 400,000 ethnic Vietnamese.

> Lon Nol hoped to use the Vietnamese as hostages against PAVN/Viet Cong activities, and the military set about rounding them up into detention camps. That was when the killing began. In towns and villages all over Cambodia, soldiers and civilians sought out their Vietnamese neighbors in order to murder them. On 15 April, the bodies of 800 Vietnamese floated down the Mekong River and into South Vietnam. [1]

Under the circumstances, the North Vietnamese allied with the Khmer Rouge and the ousted Sihanouk to take back the government from Lon Nol. In the beginning there was no sign of a genocidal regime, and the Khmer Rouges were just "comrades" supported by the Cambodian prince trying to take back his government. It was not until later that ethnic and ideological hatred turned the Khmer Rouge against their Vietnamese allies.

[1] https://en.wikipedia.org/wiki/Cambodian_Civil_War