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 …
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.
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.
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.
This was a chilling reminder of the group’s ability to strike at the heart of the country with relative ease.
CNN’s Michael Martinez contributed to this report.