Although the intentional and indiscriminate targeting of civilians is extremely common in non-international armed conflicts by national armed forces and irregular militias alike, it is now commonly represented that all or nearly all of the international laws of war – including the rule of proportionality – apply with equal vigor and scope to internal conflicts. Yet, these conclusions have little evidentiary foundation. In the absence of specific targeting rules in a treaty relating to non-international armed conflicts, the only source for more detailed guidance under international law would be customary international law. For a practice to become binding international custom, it must be sufficiently longstanding, consistent, and universal. The practice must also be accompanied by the belief that it is mandated by international law (opinio iuris sive necessitatis), as opposed to being merely optional or advisable. Better evidence is needed of whether the laws of war are aligned with state practice in non-international conflicts. In pursuit of this evidence, we have chosen to examine one specific aspect of the laws of war - the doctrine of proportionality. We are engaged in a multinational study of state customary practice of proportionality since 1945. As traditionally understood, proportionality requires military commanders to consider whether striking a given target is “expected to cause incidental loss of life, injury to civilians, damage to civilian objections or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.” The study will examine how the principle has played out - specifically, the role it plays in targeting and planning decisions as well as state responses to obvious violations of the rule - in many armed conflicts in many countries. To better understand state practice, we are using a methodology designed to gather empirical information beyond official governmental and NGO publications and news reports. Our goal for the present chapter is to examine state practice in applying this proportionality doctrine in the civil strife between the Colombian government and two armed subversive groups - the Revolutionary Armed Forces of Colombia (FARC) and the National Liberation Army (ELN) - from 1982 to present. This vicious and bloody war, waged since 1982 and ongoing today, is notable for the large number of intentional civilian deaths and property damage, but it also involves numerous incidents of allegedly indiscriminate or disproportionate attacks resulting in accidental but avoidable civilian casualties and property damage. In the end, we sought to determine, in part, whether the practice of Colombia in its war with the FARC confirms that proportionality has a customary law meaning either consistent with or divergent from traditional understandings in international conflicts. By examining incidents from this conflict it is at least possible to gain insight into the role that proportionality considerations play in targeting decisions made by the Colombian military.
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