Military exercises on an adversary's border or demonstrations in a neighbor's community are provocations, and when they succeed in provoking, those who held the "peaceful" demonstrations are guilty, as well as those who shoot first. If those conducting the "peaceful" provocations are more powerful, then their guilt is accordingly greater because the danger to the provoked side of not shooting first is correspondingly greater.
When reading the day's news, one should first consider the appropriate principle and only then allow oneself to think about the actual actors. Preventive violence is always to be deplored, but consider a policeman surrounded by visibly menacing and well armed thugs or a woman threatened with rape on a dark street. Those scenarios are very different from a nuclear armed state conducting preventive war against a non-nuclear state, indeed almost opposite extremes. The day's events need to be put in a broad comparative context and seated in concrete principle to be judged fairly.
Now consider three less clear-cut scenarios:
First, the leader of a colonial power marches through the holiest site of an oppressed and colonized minority. Does the minority have the right to attack the colonial power for this insult?______________
Second, a nuclear power with massive conventional force superiority and a reputation for barbaric violence to maintain its regional military superiority violates a neighbor's territory with military aircraft. Does the weak neighbor whose territory has been violated have the right to shoot down the planes?
Third, a vicious dictatorship watches a superpower-supported antagonist conduct massive military maneuvers right on its border. Does the dictatorship have the right to shoot first to warn off its adversary?
For a very different approach to analyzing the context, i.e., a focus on the domestic context rather than the international context, see Victor Cha's commentary on the current Korean situation in The New York Times. If the first step is to focus on context, the second step is to figure out what context is key in the mind of the actor. Even when Washington gets the first step correct, it often misunderstands the second step, frequently by erroneously assuming that the U.S. is the center of everyone's universe.