Attempted regime change by China. But they were so incompetent they got stopped cold by Vietnamese national guard troops. The regular army was clustered around Hanoi and didn't even get involved. After China took massive casualties and its offensive ran out of steam, they declared victory and left, destroying everything they could get their hands on along the way.

Then, the war was forgotten. Vietnam was America's forgotten war for over a decade, Korea is still mostly forgotten except for MAS*H, but the China-Vietnam conflict is forgotten today in China for reasons that must be obvious.