Reading about the Sino-Vietnamese War, I noticed an interesting bit: in general, people are desperately patriotic. They act strongly the second they feel their country is in danger.
Being invaded by foreign forces, Vietnam suffered greatly and its people did their best to defend themselves resulting in lots of heroic acts, some are unimaginable. The same thing can be said about almost any other revolutions, from those ancient rebellions to modern Arab Spring movements. The entire country united (at least in the northern part) and fought back with their bare hands as necessary. Winning two big wars must have made Vietnam feel invincible, especially with full support from communist countries/Russia (Soviet by then, it was one of the two superpowers at the time, their military forces rivaled those of the Americans). It’s certain that Vietnam could not sit still with Cambodia knocking on their back. With superior experiences, Vietnam could push through Cambodia’s defensive forces to teach them a lesson and let the war escalate if possible (which it did).
China was threaten when Russia and Vietnam became allies and they could easily harm China with a flank attack. The situation turned worse for China when its friend, Cambodia, was wiped out in the Cambodian–Vietnamese_War. China might have other reasons but it’s pretty obvious that China had to do something to protect itself. The best defense is a good offense and China did exactly that. They kept most of their forces at the Russian border and launched the rest to Vietnam direction. I meant what is the worst for them? If the attack fails, they clean up the northern Vietnam while sustaining some casualties. If all go well, they just go forward and take over the entire country.
So when did it begin? People are patriotic but it’s just so happen that they are greedy too, some are (way) more than others. However, it all balances out in the end I guess.
What can we do? Enjoy life when we can: play Flappy Bird, criticize each other, say sorry, rinse and repeat. And of course, fight when we must.