I’m ashamed to say that I didn’t know about that one. But then, it was so brief . . . Thought it had something to do with the Vietnamese invasion of Cambodia, though.
I think it did - at least I thought it did. IIRC the Chinese thought the Vietnamese were getting a little full of themselves by invading Cambodia. I might have my dates off though.
The Vietnamese invaded Cambodia because the Khmer Rouge had staged large numbers of cross-border attacks that killed thousands of Vietnamese civilians. The Khmer Rouge's long term objective was to recreate the Khmer empire that once ruled Vietnam before they were driven out by refugees from what is now China, over a thousand years ago. The Vietnamese objective was to topple the Khmer Rouge and replace it with a friendly government, thereby ending the relentless cross border attacks. The Chinese staged a large scale punitive invasion of Vietnam because the Vietnamese would not agree to border adjustments in China's favor, and failed to show the appropriate gratitude (i.e. grovel before China) after decades of communist Chinese military assistance for the Vietnamese communists against both France and the US. The Chinese were also irked because the Khmer Rouge was closely aligned with China, and the Vietnamese invasion of Cambodia toppled one of the China's few allies in the region.
From a moral standpoint, I'd have to say that Vietnam's invasion of Cambodia was one of the most defensible around, because it was a prophylactic war aimed at preventing further massacres of its citizens by Khmer Rouge invaders rampaging through its border provinces, that had the side benefit of interrupting the Khmer Rouge genocide that had already killed 1/3 of the Cambodian population. In contrast, China's invasion of Vietnam was a model of cynicism. China had contributed Red Guards that trained the Khmer Rouge cadres who implemented the Cambodian genocide. The invasion of Vietnam was aimed at returning the Khmer Rouge to power, despite the Khmer Rouge's genocidal record, notably against Cambodians of Chinese descent (whose numbers went down 50% after the genocide), whose well-being the Chinese claimed to champion.