States must never make civilians the object of attack and consequently never use weapons that are incapable of distinguishing between civilian and military targets. . . States do not have unlimited freedom of choice of means in the weapons they use.

...

The terrorist attacks on the World Trade Center (if not the Pentagon) on September 11, 2001 pose the legal dilemma of how to respond proportionally when the initial attack was itself unreasonable, excessive, and against civilians. Nonetheless, the suggested policy of holding entire nations accountable for the acts of a few would not appear to be lawful since collective punishment would, by definition, entail the unnecessary suffering of innocent populations.

B. Welling Hall
Professor of Politics and International Studies
Earlham College