Battling horror of ISIS: Iraq's bloody crisis up close
Updated 0632 GMT (1432 HKT) October 16, 2016
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(CNN)Thousands dead. Millions more driven from their homes. A future far from certain.
This is the situation in Iraq today.
The deep-rooted sectarian divide that resurfaced amid the chaos of Saddam Hussein's downfall created a security vacuum that ultimately allowed extremist militant groups like ISIS to flourish.
When ISIS fighters swept across Iraq in 2014, capturing major cities like Mosul, a humanitarian disaster on an unprecedented scale quickly unfolded.
CNN looks at Iraq's bloody crisis up close:
THE CRISIS IN NUMBERS ...
Around a quarter of Iraq's population urgently require aid, according to the United Nations -- a situation that has accelerated in recent months as the struggle to remove ISIS from Iraqi territory intensifies. This forces the most vulnerable to flee their homes for an uncertain future.
If they're more fortunate and manage to flee the brutality of ISIS, they end up in makeshift camps in many cases -- tens of thousands of people, many elderly or children -- without electricity and running water.
Humanitarian agencies estimate that nearly 14,000 families (up to 84,000 individuals) may have left Falluja and surrounding areas when a government offensive to retake the city began on May 23.
For weeks now, an Iraqi-led coalition has been circling Mosul, preparing to retake a city the Iraqi army lost so ignominiously in 2014. Once home to more than two million people, only around half that number remain. And many more are are expected to follow. The UN refugee agency's Iraq representative, Bruno Geddo, recently said the exodus from Mosul could be "one of the largest man-made displacement crises of recent times."
Tens of thousands of Iraqi civilians have lost their lives since 2003, though the number has spiked again under ISIS. Nearly 19,000 people were killed between January 2014 and October 2015 alone -- a toll the United Nations called "staggering."
WHY MOSUL WILL BE TOUGH TO CRACK ...
Over the last four months, soldiers from the Iraqi-led coalition have methodically toughed it out as they pressed north, liberating villages and towns along the way. At one point, they reached the Tigris River -- which flows through Mosul -- and then dropped a pontoon bridge that ISIS tried but failed to blow up with a boat packed with explosives.
So far their fighters have been pushed back, faced by opponents far more determined and organized than the Iraqi force that so easily capitulated in 2014. But the battle for Mosul itself will not be easy.
In the two years it has held the city, ISIS has built an elaborate network of defenses, including moats filled with oil that stretch around the outskirts of the city, ready to be set ablaze to obscure the vision of coalition air power.
US military officials estimate there are 3,500-5,000 ISIS fighters dug in, a mixture of Iraqis and foreign fighters.
The offensive will also be a real test of the relationship between the Iraqi security forces and Kurdish Peshmerga.
ISIS IS LOSING GROUND ...
... BUT THEY REMAIN DEADLY
With ISIS facing an inevitable defeat on the battlefield, the nature of their future threat is the subject of much debate. In recent months, the Iraq's capital has bore the brunt of what ISIS is capable of when it comes to terror attacks on civilian population centers.
A string of bombings in busy neighborhoods in Baghdad earlier this year culminated in the deadliest single attack on the city in years, when a truck packed with explosives plowed into a busy shopping district killing almost 300 people.
This was a chilling reminder of the group's ability to strike at the heart of the country with relative ease.