The spate of allegations of civilian deaths as a result of US operations in Iraq, Syria, and Yemen over the last few weeks has garnered significant interest from humanitarian groups around the world, as well as, finally, the United States Congress. Some media reports suggest that the March 17 bombing in Mosul, if true, is the single biggest civilian casualty event resulting from a U.S. airstrike since the 2003 invasion of Iraq, while multiple other reports question whether possible changes in the rules of engagement led to this overall increase in civilian deaths. The US military, however, says that a) nothing has changed in the rules of engagement; b) all allegations of civilian harm are taken seriously; and c) in war—especially when fought in populated areas—some civilians unfortunately will die.

War is hell, there can be no doubt. It’s foggy and chaotic and the innocent suffer harm, whether accidental, incidental, or intentional. It is a reality recognized through the creation of international law where we, as different people and nations, have collectively decided that some civilian harm is an acceptable, albeit tragic, part of war. But how many, and by whose hands, civilian deaths are acceptable in conflict?

The best way forward lies in understanding where law begins, where strategy calls for maximizing civilian protections—and where tactical decisions in the heat of battle can burn away those neatly drawn lines.

In warfare, civilian harm is viewed through a legal, ethical, and strategic lens. Legally, armed actors are supposed to adhere to International Humanitarian Law, or the Law of Armed Conflict, that body of international law that mandates protection for civilians. Of the Law’s four basic principles, the most amorphous is also the one that arguably most accommodates loss of civilian life—that of proportionality. The principle of proportionality states that an attack is prohibited if it is expected to cause incidental loss of civilian life, injury, or harm to property that would be excessive in relation to the concrete and direct military advantage anticipated.

If only Euclid had given us a formula. The reality is that there is no objective benchmark to help us understand the value in civilian lives of different “military advantages” even if only “concrete and direct” military benefits are considered. So is one civilian life equal to one soldier’s life in your own military unit? How about a tank, or the high point overlooking a valley? How many anticipated civilian deaths are worth the control of a city block? How many equal one dead enemy, or even the defeat of ISIS? Does it matter if those civilian deaths happen all at once in a single incident, or are spread out over a longer period of time across multiple strikes? Or does it matter who causes them?

In the real world of military operations rather than a classroom or textbook, the blurry line of proportionality looks even blurrier. American military doctrine states that military advantage need not be assessed as “immediate,” but rather in the “full context of war strategy.” So commanders, planners, and their legal advisers sitting around the figurative war map and assessing strategic and operational objectives might come to one conclusion, but an American Special Forces sergeant advising a squad of Iraqi infantrymen pinned down by an ISIS sniper – though he has the very same legal requirements as do the commanders and lawyers in assessing proportionality – may come to a very different one: How does eliminating this target give me an advantage right now?

Examining these issues on today’s battlefields, does killing an ISIS sniper perched upon a building in Mosul (and preventing the sergeant from taking the city block in front of him) outweigh the possibility that dozens of civilians might die in the attack—an outcome that could provide ISIS an easy message to use in its recruiting endeavors, and perhaps creating two dozen more ISIS snipers in some other city in some point in the future? What is the priority, and who must make this assessment?

This, arguably, is a strategic assessment and not a legal one, but it is impossible to remove strategy from the Law of War – they are part and parcel. And soldiers on the ground frequently understand “proportionality” not in the context of the law, or even necessarily in support of the greater strategic objective, but rather in the context of a commander’s intent, relayed at the lowest level: if taking this city block is my priority in defeating ISIS, then I am taking this city block.

If, in fact, this is the assessment at the tactical level, it effectively negates the strategic goal of defeating ISIS everywhere, not just in one city. Because as long as civilians are not visibly present to that soldier on the ground, a “see enemy, kill enemy” approach to street fighting is likely, increasing the probability of catastrophic civilian harm events like those this past month in Raqqa and Mosul.

In contrast, if not causing civilian harm is the priority, then the soldier on the ground might rethink a decision to call in an airstrike to kill that one sniper and find another way to overcome the threat. This scenario illustrates the conundrum facing American commanders: They must act with aggression and violence in order to quickly defeat ISIS, thereby saving local civilians—and, ostensibly, also those at home in the US—from their barbarism; but by acting with aggression and violence, US operations will kill more civilians, thereby providing ISIS fuel to flame its ideology – a key to recruiting more fighters.

So which is more palatable? The equation of a quick and dirty fight for Mosul might favor accepting significant civilian loss of life over the slow grind of a long, drawn-out street fight—a speculative argument not far removed from “in order to save the village, one must burn the village.” But the strategic value that catastrophic events, like the one in Mosul, have for the enemy should be acknowledged and included not just at the highest levels of the planning process, but down to the soldier on the ground who executes the operational plan.

As emphasized by Secretary of Defense James Mattis, Gen. Joseph L. Votel, and Lt. Gen. Stephen Townsend, the US military sets a high bar for protecting civilians during combat operations, particularly in comparison to the enemy, who kill indiscriminately and regularly commit acts of inhumanity. But the war against ISIS is not akin to outrunning an angry bear, where you simply have to be faster than the guy you’re with. This is a war where generals and policymakers tout the importance of protecting civilian lives as not just the right and ethical thing to do, but as a strategic imperative – perhaps the most important strategic imperative – in defeating ISIS.

No civilian harm in armed conflict is a patently unreasonable expectation. Civilians are killed and injured in armed conflict, and surely always will be. But who kills them, and the unnecessary manner in which they do so, is just as important. Deciding what are the acceptable costs of human life, both within the law as well as within the strategic parameters of fighting a war where civilian perceptions are key to long-term victory, deserves a sustained second look.


Photo: A street that was partially destroyed during the offensive to recapture the city of Mosul from Islamic State militants, on October 23, 2016 in Bartella, Iraq – Carl Court/Getty