Proportionality is intimately linked to the overarching concepts of self-defense, lawful force, and the controlled application of violence. It is one of the most visible facets of humanitarian law designed to reduce unnecessary human suffering and avoid excessive damage to property, and the natural environment. However, its application has come under renewed scrutiny and sustained controversy as a result of wars against non-state actors and from the extensive use of drones, human shields, cyber war techniques, and counterinsurgency tactics.

Proportionality in International Law...