In the next three chapters, I will reconceptualize several of the traditional jus ad bellum principles for use in international criminal law. In this respect, I will return to the discussions in the first chapters about how to justify war morally and legally. The guiding idea will be that for purposes of criminal trials of individuals for the crime of aggression, a somewhat different standard of what counts as defensive and what counts as aggressive war may be advisable. We may want a more expansive idea of aggressive war if what we are interested in is merely condemning States for their behavior. But when we come to the question of what standard to use in criminal trials there may be good reasons to focus only on the most egregious cases of aggression. In this respect, then, it also would make sense to reconceptualize the traditional principles of jus ad bellum that mark the divide between aggressive and defensive war.

I will begin with a normative principle that is not normally listed as a jus ad bellum principle, the principle of priority or first strike. This principle is often cited as one of the main normative principles in international legal discussions, but as we will see properly it is really a preliminary way of understanding the just cause principle, the subject of the next chapter.