The US-led coalition campaign to destroy the Islamic State group in Iraq and Syria enters its fourth year this week, and the Pentagon believes the jihadists' defeat is inevitable.

On August 8, 2014 two FA-18 jets launched from the USS George W. Bush aircraft carrier in the Gulf and dropped 500-pound laser-guided bombs on IS fighters near Arbil in northern Iraq.

The action marked the beginning of an intense aerial bombardment that was later augmented by the training and equipping of local forces to fight IS, first in Iraq and then in Syria.

IS burst into the limelight earlier in 2014 as it swept across northern Iraq and Syria, seizing major cities including Mosul and Raqa, and leaving a trail of slaughter and barbarity in its wake.

At the height of its advance, IS held about 40,000 square miles (104,000 square kilometers) of territory and even threatened Baghdad, with many Iraqi military units collapsing in disarray as the jihadists approached.

"They had eight million people who were being ruthlessly held captive by their rule and living in misery, many forced into refugee status and depravity," Pentagon spokesman Navy Captain Jeff Davis said.

In the three years since the campaign began, 70 percent of the territory IS once held in Iraq has been recaptured, and 50 percent in Syria.

"Not one inch of that territory that we have liberated has been retaken by ISIS," Davis said.

"ISIS is facing its inevitable defeat. We will win and they will lose."

The US-led coalition comprises 69 countries, though only a handful of these partners are participating in the air campaign or training missions.

Even though experts foresee the eventual collapse of IS's self-declared "caliphate," the jihadists have fought back by calling on followers to launch terror attacks across the globe.

As of July 26, 2017, the coalition had conducted 13,221 strikes in Iraq, and 10,701 strikes in Syria, for a total of 23,922 strikes at a daily cost averaging $13.6 million.

The fight against IS has seen constant bombing sorties, often in urban areas.

The coalition has acknowledged killing 624 civilians to date, though observers say the real number is much higher.

"While this is the most precise campaign in the history of warfare, civilians do die in war and that's the sad truth," Davis said.  Source: AFP