The US has not ratified the API. The next task is hence to establish the customary definition of a legitimate target of attack. Customary law is defined as a ‘general practice accepted as law’. The 168 ratifications of the API bear testimony to the fact that the definition of a legitimate target that was hammered out during the diplomatic conference and adopted on 8 June 1977 is widely accepted as law. A universally ratified treaty provides a strong presumption that customary law is congruent with its positive counterpart. Yet the API, contrary to the Geneva Conventions, is not universally ratified. Among other countries, Afghanistan, Azerbaijan, Egypt, Eritrea, India, Iran, Iraq, Israel, Pakistan and the former Federal Republic of Yugoslavia, like the US, are not parties to the treaty, suggesting they do not accept it as binding IL. While not a large group, it includes the states that have most often been involved in interstate armed conflict in the recent past. In fact, with one exception there has never been an international armed conflict in which the Protocol was applicable among parties on different sides in the war since its entry into force in 1979. The practice of warfare is hence dominated by states that are not bound by the positive definition of a legitimate target of attack. Do these states disagree with the way in which the principles of proportionality and distinction are enshrined in the treaty? If they do and their practice hence diverges from positive law, what is the customary definition of a legitimate target of attack?

The definition of a legitimate target of attack

The first step in attempting to establish the customary definition of a legitimate target of attack is an investigation of the status of proportionality and distinction pre-positivisation, meaning before the diplomatic conference was convened in 1971. To that end I will briefly sketch the principles’ respective histories. This endeavour prepares the ground for an assessment of how the API may have influenced the customary definition of a legitimate target of attack.