A year ago this month, Islamic State (also known as IS, ISIS, or ISIL) began a systematic program of capturing women and girls for the purposes of rape, forced marriage, and sexual slavery. Yesterday, the New York Times brought renewed attention to the war crimes in an article examining how IS enshrines a theology of rape.

Here are five facts you should know about how IS views and justifies the practice of sexual slavery:

1.IS considers rape of sex slaves to be a form of worship — In the New York Times article, a Yazidi girl was was enslaved by IS claims:

“Every time that he came to rape me, he would pray,” said F, a 15-year-old girl who was captured on the shoulder of Mount Sinjar one year ago and was sold to an Iraqi fighter in his 20s. Like some others interviewed by The New York Times, she wanted to be identified only by her first initial because of the shame associated with rape.

“He kept telling me this is ibadah,” she said, using a term from Islamic scripture meaning worship.

2. IS has an eschatological justification for sex slavery

Islamic State publishes a glossy propaganda magazine called Dabiq. In the October 2014 issue, IS included an article titled “The Revival Of Slavery Before The Hour,” which explains the justification for sex slavery.

In Islamic terminology the “hour” refers to the Day of Judgment, a time of reckoning either for an individual upon death or on mankind. According the article, IS asked its own Sharī’ah (Islamic law) scholars to render a verdict on whether the Yazidis could be enslaved. They determined that “enslavement of the apostate women” was not only justified by the Quran but was a sign prefiguring the Day of Judgment.

3. IS condones the rape of young girls — Last fall the Research and Fatwa Department of the Islamic State (ISIS) released a pamphlet on the topic of female captives and slaves:

“Question 13: Is it permissible to have intercourse with a female slave who has not reached puberty?

“It is permissible to have intercourse with the female slave who hasn’t reached puberty if she is fit for intercourse; however if she is not fit for intercourse, then it is enough to enjoy her without intercourse.”

4. Acquisition of sex slaves is used as a recruiting tool —

As the New York Times article notes, the practice of slavery has e an established recruiting tool to lure men from deeply conservative Muslim societies, where casual sex is taboo and dating is forbidden. Capturing sex slaves has e nearly as important for IS’s objectives as capturing territory.

5. IS has about 3,000 girls and women engaged in sexual slavery — According to Human Rights Watch, the Office of the United Nations High Commissioner for Human Rights stated in its report on March 13, 2015 that about 3,000 people, mainly Yazidis, allegedly remain in ISIS captivity. However, local officials, service providers, munity activists estimate that the number of Yazidis still held is much higher.