Disproportionate Attack

The concept of a disproportionate attack is a cornerstone of the principle of proportionality in international humanitarian law (IHL). It is codified in Article 51(5)(b) of Additional Protocol I (1977) to the Geneva Conventions, which defines as indiscriminate "an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated." Article 57 imposes a parallel obligation on commanders to take precautions and cancel or suspend attacks that would breach this rule.

The assessment is prospective and contextual: it asks what a reasonable commander, with the information available at the time, anticipated — not what actually occurred. Two variables must be weighed:

• Expected incidental civilian harm (deaths, injuries, damage to civilian objects, and, increasingly, reverberating effects on infrastructure such as water and electricity).
• Concrete and direct military advantage anticipated — meaning a tangible, near-term gain, not speculative or purely political benefit.

There is no fixed numerical ratio. The standard is qualitative, which makes enforcement difficult. The Rome Statute of the International Criminal Court (Article 8(2)(b)(iv)) criminalises intentionally launching an attack in the knowledge that it will cause incidental civilian harm "clearly excessive" in relation to the military advantage — a slightly higher threshold than Protocol I.

The rule applies regardless of whether the target itself is lawful; even a legitimate military objective cannot be struck if the collateral civilian cost is excessive. It also applies in non-international armed conflicts as customary IHL, per the ICRC Customary IHL Study (2005), Rule 14.

Disproportionate attacks are distinct from indiscriminate attacks (which fail to distinguish between civilians and combatants at all) and from direct attacks on civilians, though the categories often overlap in practice. Investigations by UN commissions of inquiry, the ICC, and domestic courts routinely turn on proportionality assessments, which remain among the most contested areas of IHL.