U.S. Marines aid a comrade during fighting on the outskirts of Baghdad in April 2003. (Laurent Rebours/AP)

Tens of thousands of people died fighting in the Iraq War, which began 15 years ago Tuesday. Nearly 5,000 of them were U.S. service members. Tens of thousands were insurgents battling the transitional Iraqi government put in place after the ouster of Saddam Hussein.

But that figure obscures the actual number of deaths attributable to the conflict. During the war and during the Islamic State militant group’s occupation of as much as a third of the country in recent years, the number of deaths runs into the hundreds of thousands, including civilians killed as a result of violence and, more broadly, those who died because of the collapse of infrastructure and services in Iraq resulting from the ongoing conflict.

A precise death toll, though, is almost impossible to calculate.

One of the best resources for tracking the number of civilians killed is the site Iraq Body Count, which has tallied violent deaths in the country from news reports since the conflict began. Data from IBC shows the three phases of the conflict clearly: the initial invasion, the collapse of security in the country that followed and the emergence of the Islamic State in the ensuing instability.

About 6 in 10 civilian deaths at the hands of coalition forces from 2003 to 2011 were a function of airstrikes, according to IBC data. During the Islamic State period, all of the civilian deaths caused by coalition forces were from the air. Most of the civilian deaths are attributed to unknown actors during the initial span of the war (which President Barack Obama declared over in 2011).

When the Islamic State declared a caliphate from the city of Mosul in June 2014, the group became the main cause of civilian deaths in Iraq, with more civilians dying that month than in any month during the war. In June 2014, IBC tallied nearly 4,100 civilian deaths. Over the course of the year, more than 20,000 people died. It is important to consider that this is 20,000 deaths in a country of about 35 million. In 2014, about 5.8 of every 10,000 Iraqis died as a result of violence. In 2006, shortly before President George W. Bush announced the surge of U.S. troops, the figure was 10.7 per 10,000 people.

We can put that into the context of the U.S. population, which was more than 10 times as large at the outset of the war.

  • 2004: 4.5 out of every 10,000 Iraqis killed. Equivalent to 130,000 American deaths — the population of McKinney, Tex., in 2010.
  • 2005: 6.1 out of every 10,000 Iraqis killed. Equivalent to 181,000 American deaths — like eliminating Tallahassee.
  • 2006: 10.7 out of every 10,000 Iraqis. Equivalent to 318,000 American deaths — the population of St. Louis.
  • 2007: 9.2 out of every 10,000 Iraqis. Equivalent to 277,000 American deaths — the population of Newark.

IBC’s estimates may also be low.

A 2013 analysis by researchers from the United States, Iraq and Canada took a broader look at the likely death toll from the war. Their findings:

From March 1, 2003, to June 30, 2011, the crude death rate in Iraq was 4.55 per 1,000 person-years (95% uncertainty interval 3.74-5.27), more than 0.5 times higher than the death rate during the 26-mo period preceding the war, resulting in approximately 405,000 (95% uncertainty interval 48,000—751,000) excess deaths attributable to the conflict. Among adults, the risk of death rose 0.7 times higher for women and 2.9 times higher for men between the prewar period (January 1, 2001, to February 28, 2003) and the peak of the war (2005—2006). We estimate that more than 60% of excess deaths were directly attributable to violence, with the rest associated with the collapse of infrastructure and other indirect, but war-related, causes.

We bolded the key phrase: About 400,000 deaths were probably attributable to the conflict from 2003 to 2011, about 240,000 of them a result of violence and 160,000 from war-related causes. The 240,000-death estimate caused by the conflict is about twice the IBC estimate. (That study also estimated an additional 55,000 deaths among Iraqis who fled the country during the conflict.)

That takes us only to 2011. In the seven years since, IBC estimates, there were 82,000 additional deaths resulting from the conflict in Iraq — just among civilians.

It seems likely that the death toll in the past 15 years easily exceeded half a million Iraqis, but how much higher is hard to determine.

If we assume that 600,000 people died, that is about equivalent to the population of Washington, D.C., in 2010. As if every man, woman and child in the District of Columbia were killed in war, died as a result of failing infrastructure or were killed by Islamic State terrorists.

This article was corrected to remove a reference to a 2006 study that has since been challenged.