The hoary doctrine of “proportionality” from the “just war” theory is being sorely tested by the wars in the Middle East and Ukraine.

The premise of this theory, as first expounded in the West by Saint Augustine and later elaborated on by Thomas Aquinas, is that the use of force by governments against other states, generally morally prohibited, is justifiable under certain circumstances. It is about defensive war, undertaken in response to acts of aggression by others.

A key element in just war is the notion of proportionality — that the response to aggression must be in a certain sense symmetrical. The force used must not exceed what is necessary.

In the modern age, the degree of military destructiveness has exponentially expanded with the advance of technology. The use of certain weapons systems, most notably weapons of mass destruction — nuclear, biological and chemical — inherently violates the requirement of proportionality. Their use is so horrific that such weapons have generally been prohibited, deemed to constitute war crimes or crimes against humanity.

But beyond the hardware of weapons systems, the operational techniques used in warfighting can also be........

© The Hill