Scattered reports from inside ISIS-controlled territory have painted an awful picture of life under the militant group's rule. But a brand-new UN report, compiled from interviews with 300 people who have lived or currently are living in ISIS-controlled Syria, gives us a systematic look at the militant group's reign.

And it is horrifying.

This isn't just because the behavior documented is terrible, though it is. It's that the UN report documents a strategy, not just random brutality or religious fanaticism. ISIS's ultraviolence is designed to cement its rule by terrifying the population into submission. And it might be working.

Everyday life in ISIS territory is a horror show

Consider this testimony from an anonymous father living in Deir ez Zor, in the eastern part of the country. Walking with his son, he saw two men strung up on a cross. "Both victims' hands were tied to each side of the improvised cross," the man reports. "I went to read the placards. On the first one it read, 'This is the fate of those who fight against us.'"

He somehow had to explain this to his child. "I realized that my 7-year-old son was next to me, still holding my hand and watching this horrifying scene. He later asked me, 'Why were they there? Why was their blood on the heads and bodies?' I had to lie to him and say they were waiting for ambulances to come and rescue them."

According to the UN, this terrible public killing is terrifyingly common: "ISIS has beheaded, shot and stoned men, women and children in public spaces in towns and villages across northeastern Syria." UN investigators found a consistent pattern, where ISIS "encourages" citizens to attend public executions — often at gunpoint.

"Witnesses saw...heads placed on spikes along park railings"

"Following the killings, the corpses are placed on public display, often on crosses, for up to three days, serving as a warning to local residents," the UN reports. "Witnesses saw scenes of still-bleeding bodies hanging from crosses and of heads placed on spikes along park railings."

And that's how the group treats male Sunni residents — to say nothing of minorities, women, and children. ISIS's genocidal campaign against Iraqi minorities, which include systematic rape and enslavement of female members of the groups, is well-known.

Also well known are the strict restrictions it places on even Sunni women in its territory. According to the UN, women are confined to their homes at almost all times. On the rare occasions they're permitted outside, "ISIS regulations dictate what women must wear, with whom they may socialize, and where they may work." Women who break the rules are regularly beaten and even killed.

Its abuse of children is less well known, but no less horrifying. According to the UN report, ISIS has turned Syria's schools into indoctrination camps. In Raqqa, ISIS's de facto capital, children are sat down for mass screenings of ISIS soldiers executing prisoners of war. Children are instructed to inform on their parents if they violate ISIS strictures.

There's a terrible logic behind this violence

This all seems utterly inhuman. But it's not random. Unlike some human rights abusers, ISIS doesn't hide its brutality — in fact, it makes the horror impossible to ignore. There's a terrible logic at work here. "By publicizing its brutality," the UN concludes, "the so-called ISIS seeks to convey its authority over its areas of control, to show its strength to attract recruits, and to threaten any individuals, groups or States that challenge its ideology."

Such violence isn't rare in war zones. According to Stathis Kalyvas, a Yale professor who studies civil wars, rebel groups understand that civilian defection is an existential threat to their rule. Their violence is generally targeted to coerce civilian cooperation with the group — which is why ISIS labels the people it publicly executes as traitors. The message: defect to the government or a rebel group, and you'll pay.

ISIS also pairs its brutality with social service provision: they provide food, electricity, medical care, and some semblance of a justice system. Buy people's loyalty when you can, and force it when you can't.

So far, this might actually be working. A recent New York Times report suggested Raqqa residents were angry about American strikes on ISIS targets because they made it harder for ISIS to maintain order and public services in the city. But ISIS's absurd brutality has provoked backlashes before. In 2006, back when ISIS was al-Qaeda in Iraq, a rebellion that was partly inspired by the group's brutality nearly destroyed it.