[retrac]

The most egregious acts can be downplayed or politely ignored, if the aggrieved party really wishes to avoid war. On the other hand, the smallest provocation can serve as a justification for war, if the aggrieved party wants war.

North Korea regularly shells South Korea, sometimes killing South Korean civilians. It's absolutely a cause for war, and they might indeed be justified, in a sense, with breaking the ceasefire and marching on Pyongyang the next time NK does so. But they will have to live with the war that would cause.