IIRC. It was primarily the USSR which backed the North Vietnamese. By the early 70’s the communist block had split between the USSR and China. Vietnam was USSR

IIRC. It was primarily the USSR which backed the North Vietnamese. By the early 70’s the communist block had split between the USSR and China. Vietnam was USSR not Chinese ally. Not long after the end of the Vietnam war, China attacked Vietnam (https://en.m.wikipedia.org/wiki/Sino-Vietnamese_War https://en.m.wikipedia.org/wiki/Sino-Vietnamese_War) ostensibly as the Vietnamese had attacked Cambodia, by this stage supported by China (and the US) to dispose the Khmer Rouge. Suffice to say it went badly for the PLA and thanks to the Vietnamese the Khmer Rouge was ultimately disposed.