The danger must be immediate, which is the first essential point. Though it must be confessed that when an assailant seizes any weapon with an apparent intention to kill me I have a right to anticipate and prevent the danger. For in the moral as well as the natural system of things there is no point without some breadth. But they are themselves much mistaken, and mislead others, who maintain that any degree of fear ought to be a ground for killing another, to prevent his supposed intention. It is a very just observation made by Cicero in his first book of De Oficiis, that many wrongs proceed from fear; as when the person, who intends to hurt another, apprehends some danger to himself unless he took the preventive step. Clearchus, in Xenophon, says, I have known some men, who partly through misrepresentation, and partly through suspicion, dreading one another, in order to prevent the supposed intentions of their adversaries, have committed the most enormous cruelties against those who neither designed, nor wished them any harm.
—Hugo Grotius, De jure belli ac pacis bk 2, ch 1, sec 5 (1625)(Grotius discusses the manipulation of fear to justify pre-emptive war-making)(S.H. transl.), in the Liberty Fund ed., vol. 2, pp. 398-99 (J. Barbeyrac transl.)