Fighting in densely populated areas poses a number of significant challenges to forces trying to adhere to the rules that govern warfare. Even assuming that international humanitarian law (IHL) is respected, the cumulative effect of urban warfare inevitably leads to human suffering. Nowhere is the tension between the military necessity to defeat an enemy and challenges in protecting civilians more apparent than in cities like Aleppo, Donetsk, Mosul, Raqqa, Sana, and Taiz.

The fight to reclaim Mosul from the Islamic State (or ISIS) is being touted as one of the most significant urban battles since World War II. It is also a case study of the significant challenges in fighting in a densely populated area. The fight in Mosul, with a population of over 1.8 million spread between east and western Mosul separated by the Tigris river, involved primarily the Iraqi Security Forces (ISF), who, depending on the unit, have different levels of training, weapons, and competencies, and the U.S.-led anti-ISIS coalition, which mostly used air strikes.

Operations began in October 2016, with the Kurdish Peshmerga and other pro-government forces engaged outside Mosul city, and ended with the capture of the Old City of West Mosul in July 2017. West Mosul’s dense population of 750,000-800,000 people, old buildings, and narrow streets made operations difficult and placed civilian men, women, and children at heightened risk. ISIS prevented many civilians from leaving West Mosul and used them as human shields. In July, when ISIS lost control of Mosul—three years after it overran Iraqi forces—it was a significant victory for the Iraqi people. Many civilians died and remain buried under the rubble in the Old City. More than 800,000 were displaced, and 99 percent of West Mosul was destroyed, this is in contrast to East Mosul where destruction was significantly less.

In Mosul, the military objective to defeat ISIS was intermingled with the larger goal of protecting civilians. While Baghdad issued guidance to limit the use of heavy weapons, such as artillery, in populated areas, all forces did not adhere it to. Some ISF units used artillery and improvised rocket assisted munitions (IRAMs) in western Mosul. Also, while some ISF members, such as the Counter Terrorism Service (CTS), received training from the coalition in conducting complex urban operations and performed with more discipline, other units or individual soldiers did not, including on treatment of ISIS members. As the campaign continued, Iraqi forces sustained high casualties from ISIS suicide attacks including while trying to evacuate civilians. 

Planning for any military operation is complex, but the presence of thousands of civilians in an urban environment introduces additional considerations—in particular, the need to adhere to IHL’s principle of proportionality. Processes governing when to engage targets of opportunity (dynamic strikes), or when supporting troops under attack, are even more challenging and need consistent review and adjustment to ensure measures are being taken to reduce incidental harm. These challenges were compounded in Mosul by ISIS tactics designed to cause mass casualties. These included booby-trapping roads and buildings with improvised explosive devices (IEDs), deliberately entrapping and killing civilians who tried to leave, and using them as human shields when attacking Iraqi or coalition forces. ISIS’ unlawful behavior however, does not relieve ISF or the coalition of its obligations under IHL, which prohibit indiscriminate or disproportionate attacks. Armed forces must “take all feasible precautions” to avoid harming civilians and civilian objects and “refrain from an attack which may be expected to cause incidental loss of civilian life, injury to civilians or damage to civilian objects or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.”

When used in urban settings such as Mosul, the use of explosive weapons with “wide-area effects”—large bombs, indirect fire weapons (rockets, artillery, mortars), and multi-barrel rocket launchers—is not expressly prohibited under IHL, but they endanger civilians. They can kill and injure civilians through blast and fragmentation, destroy electrical and water treatment plants, and sanitation infrastructure. The second and third order effects of using such weapons in cities, where critical infrastructure is interdependent, is evident. For example, destroying electrical transformers means a hospital cannot rely on electricity and provide life-saving treatment. Or water treatment facilities cannot operate, disrupting the water supply and increasing the spread of diseases.

Doctors, whom my colleagues and I met in June in Mosul, described patient injuries consistent with the use of bombs, shrapnel from mortars, artillery, IEDs, and gunshots. Precision-guided munitions, even when properly calibrated, caused civilian harm in Mosul—particularly given ISIS tactics and population density. For instance, the use of a 500-pound precision-guided munition against two ISIS snipers in al-Jadida—even though the U.S. military said it was calibrated to damage only one story of a building—destroyed the entire building, killing 105 civilians. The U.S. military said ISIS had booby-trapped the building with explosives.

“Death was all but guaranteed,” said Hanifa who described how she fled Zinjili district in West Mosul in June. “We could die either by ISIS sniper or IED or shelled or buried by bombs.”

The complexity of the battle for Mosul, compounded by ISIS tactics to cause civilian casualties, is a reminder that armed forces must continue to assess and adjust tactics to minimize civilian harm in densely populated areas, including in their choice and use of weapons.

Below is a list of legal, policy, and operational practices, although not exhaustive, adopted by some militaries to reduce civilian harm in urban warfare:


  • Train all security forces in the selection and use of a variety of means and methods of warfare in populated areas, including on technical capabilities of weapons at their disposal, and their foreseeable effects on civilians and infrastructure in urban areas;
  • Train all security forces in situation-specific urban warfare tactics and protection of civilians with emphasis on clearing and holding areas, and evacuating civilians safely.

Commanders responsibility to reduce civilian harm:

  • Commanders should issue guidance stressing the primacy of protecting civilians and civilian objects;
  • In any attack, commanders should know the type and size of munition used, their blast and fragmentation range or effects, their delivery system, the distance from which weapon was launched, as well as the timing and angle of the attack;
  • Commanders should anticipate incidental harm from the use of certain weapons in collateral damage estimates and undertake battle damage assessments, including accounts of civilian harm, in order to adjust tactics.

Practices to reduce civilian harm in urban areas:

  • Issue guidance to armed forces to avoid, when feasible, using explosive weapons in densely populated areas that are unguided or have a large destructive radius;
  • Ensure intelligence, surveillance, and patterns of life on population movements are consistently improved;
  • Adjust timing of attacks to decrease likelihood of civilian presence;
  • Cancel or suspend an attack, particularly air strikes, if a planned attack would violate the rules of distinction and proportionality;
  • Avoid, where feasible, air strikes in densely populated areas and require higher command approval for such attacks;
  • Explore alternatives to indirect fire and air strikes, such as direct fire through properly trained ground forces, where possible;
  • Establish safe and secure evacuation routes in coordination with humanitarian actors;
  • Pace military campaigns to take into account civilians’ presence.

ISIS control over Mosul has been degraded. An examination of what additional measures to reduce civilian harm during the fight needs further analysis, learning, and application for urban operations including future operations in Iraq, but also in Raqqa, Syria. Lessons from Mosul must be applied to Raqqa, where U.S. trained Syrian Democratic Forces (SDF) backed by coalition air support, are fighting ISIS in a populated city and facing similar ISIS tactics as noted above, but have had even less training then Iraqi CTS in conducting complex urban operations. Precautionary measures including choice of weapons in populated areas, safe evacuation of civilians, and pace of operations must be at the forefront for military planners and commanders in order to reduce civilian harm.

Image: Getty/ Martyn Aim