BAGHDAD — As the fight for the Iraqi city of Mosul drags on, many might ask: Why has it taken the combined militaries of the United States and Iraq backed by an international coalition more than two years to dislodge a relatively small force of militants lacking heavy weaponry?
Donald Trump raised the question during his campaign, promising to turn up the heat against the Islamic State as president. Now the growing controversy over the high number of civilian casualties believed caused by recent US airstrikes has touched on a major part of the answer: The militants are mingled among tens of thousands of civilians in Mosul, and they are willing to take the population down with them.
Inevitably, the more force brought to bear to crush the fighters, the greater the danger civilians will be killed.
To avoid that, strikes must be more surgical and more cautiously used, and the battle turns to street-by-street fighting where the technological edge is often neutralized. Minimizing civilian deaths is more than just a humanitarian concern: Heavy bloodshed can fuel public resentments that push some to join militant groups.
Another factor is whether the extremists have support from at least part of the population. It’s even further complicated if they can claim to be fighting for national liberation — as, for example, with the Hamas group in its battles with Israel in Gaza. In Iraq and Syria, the Islamic State clearly holds the population hostage in many cases, but it also seeks to sway support by claiming to defend Sunnis against a mostly Shi’ite force from Baghdad.
After a March 17 explosion that residents say killed at least 100 people in Mosul, the US military acknowledged an airstrike was involved. But the top commander of US forces in Iraq said investigations may reveal a more complicated explanation, including the possibility that militants rigged the building with explosives after forcing civilians inside.
Army Lieutenant General Stephen Townsend said recent civilian casualties in Mosul were ‘‘fairly predictable’’ given the densely populated urban neighborhoods the Islamic State fighters are defending against Iraqi troops.
Over the past 2½ years, Iraqi forces backed by US special forces and coalition airstrikes have managed to push the Islamic State out of most of the territory they overran in the summer of 2014 — retaking three major cities and numerous smaller communities. The fight for Mosul, launched in mid-October, has been the longest battle yet.
With each fight, the Islamic State has adapted its use of civilians as human shields, creating increasingly deadly battlefields.
In Tikrit and Sinjar, the Islamic State let the population flee early on, allowing Iraqi and coalition forces to liberally use airstrikes and artillery to retake the areas by the fall of 2015.
The Islamic State then tightened its grip on other cities and towns. It locked down Ramadi in western Anbar province with checkpoints to prevent civilians from fleeing. Only those with serious health conditions were allowed out — and only if they left behind a relative, property, or thousands of dollars to guarantee their return.
After Iraqi forces punched into Ramadi, fleeing Islamic State fighters forced civilians to go with them to thwart airstrikes. Moving west along the Euphrates River, Iraq’s military responded to the use of human shields by largely emptying towns of their populations as they retook territory. The massive displacement resulted in humanitarian crises. Thousands were left without shelter and little food or water in desert camps.
So the government changed tactics. It asked civilians to stay in their homes, a decision that was controversial with commanders faced with clearing militants from dense residential areas.
In Mosul, an estimated 1 million people were in the city when Iraqi forces breached its eastern edge. Islamic State fighters fired from the rooftops of homes where civilians sheltered, targeting those who fled with mortars and gunfire. In denser neighborhoods, even precision munitions inflicted heavy casualties.
