In 1979 when the Chinese attacked Vietnam they barely penetrated inside Vietnamese territory before retreating back into China. The ability of the Vietnamese to hold back the Chinese invasion was all the more remarkable as unlike the Chinese, Vietnam's front line troops were elsewhere in Cambodia fighting the Khmer Rouge who's government they had mercifully overthrown.

The Chinese failed in their objectives and the Khmer Rouge never regained control (despite also receiving support from Britain and the US)

I cycled the border last year. Its very much changed now lots of Chinese holiday makers. The locals took more photos of us than we did of them. Also visited the Hanoi war museum. The Vietnam war with the US is covered very honestly but its interesting to note that North Vietnams interventions in Cambodia and China’s attack receive just 4 very poor black and white photos. Their so bad its impossible to tell what’s even in the photos. No names or locations. The descriptions don’t even name China despite it being a victory (or more accurately a Chinese failure). Simply says Northern and Western Border 1979. It’s a sensitive period for them something I think they genuinely want to see firmly in the past.