IIRC, the Annamese and the Chinese have been at war on and off for centuries.
That's millennia, two of them.
Yes, my ancestral homeland had shaken off Chinese rule in 939 AD and since then a shaky relationship ensues to this day, even though they share similar cultural customs, fairly conservative by today’s liberal standards (really?).
And now sandwiched between them is a ten or eleven figure sum jackpot of black gold in the vicinity of the Spratly Islands that could make or break a nation’s economy.