In Cosmopolitan today, I write about the tragic fate of two teenage best friends in Iraq. Hengi Abdullah only narrowly escaped the Islamic State, and today, she struggles to provide for her parents and 10 siblings, living as a destitute refugee in Lalesh, the religious capital of the Yazidis.

Meanwhile, her best friend “Sara”—also 18, a high school senior who dreamed of becoming a math teacher—was abducted by the Islamic State and remains in captivity.

The jihadis shot 22 adults in Hengi and Sara’s extended family, killing fathers before their daughters’ eyes. The Islamic State captured six of Hengi’s female cousins, Sara included — all students, the eldest 22, the youngest 14.

Hengi knows a bit about Sara’s fate only because one of those cousins escaped, calling her recently from a mobile phone in the town of Tal-Afar, about 30 miles west of Mosul. Sara and her other cousins, the cousin said, were being used as sex slaves.

She said that the women were being raped, asked for help,” Hengi says. Her face grows grim as she continues: “She said [the Islamic State] planned to take them to Syria, give them as a gift [to other men]. She started crying on the phone and asked us, ‘Please, find a way to help us. We cannot endure this. They forced us to convert to Islam, made us wear plaques [signifying conversion] around our necks.’ She said, ‘Please, tell the airstrikes to kill all of us. It’s better than being with them, because we cannot endure any more.’ … My uncle’s daughter said on the phone, ‘We saw them sell girls to other countries. We are very tired. They just gave us food once, and they hit the women.’”

Right now, more than 1,000 women—and by some estimates, as many as 7,000—remain in the hands of the Islamic State. They suffer horrific rapes and beatings.

As I write for the upcoming print issue of National Review, for the Islamic State, rape isn’t just about sex. It’s a deliberate tool of war, employed with chilling calculation.

The Islamic State publicizes its sexual violence to terrify its enemies, making men think twice about leaving families behind to fight back. Furthermore, it persuades young men to join the Islamic State by enticing them with the promise of young women, and it sells captives as slaves to raise funds.

Read my Cosmopolitan story here, and look for my article in the upcoming magazine edition of National Review.

— Jillian Kay Melchior is a Thomas L. Rhodes Fellow for the Franklin Center for Government and Public Integrity and a senior fellow for the Independent Women’s Forum.