The principle of proportionality is a fundamental component of IHL, based on the notion that parties to an armed conflict do not have unlimited means in which to exact damage on an enemy. Nonetheless, civilian casualties during conflict are more than an on the ground reality, they are a consequence of a complex and ambiguous legal calculus recognized during hostilities. So how does IHL control excessive casualties? Article 51 (5)(b) of Additional Protocol I places this responsibility on the attacker, justifying resulting incidental civilian casualties and damage only if the concrete and direct military advantage anticipated is greater. Operationally this proportionality calculus has proven problematic. Especially difficult and commonly disputed is whether proportionality must take into account the entire conflict timeframe. This critical uncertainty can pose an incredible strain on governments, militaries and IHL. Furthermore, this ambiguity can result in additional casualties.
The challenges surrounding excessive casualties were discussed at NBOL’s 2013 workshop - The Operationalization of the Law: Enhancing the Symmetry between IHL and Military Operational Art - hosted at the ICT’s 13th World Summit on Counter-Terrorism.