Friday is usually the most peaceful day in the Egyptian week, a day most often reserved for time with family. This Friday in particular—the last day before the start of Ramadan—should have been a time of calm reflection and prayer in Egypt. Instead, gunmen killed at least 24 Coptic Christians as they made their way via bus to a monastery in Minya, south of Cairo.

Copts are the largest Christian group in the Middle East, and they represent about 10 percent of the population in Egypt. This is not the first attack that has taken aim at Christians in the country, but it is one of the most shocking, with a high death toll and children among the targets. Sadly, given ISIS’s express declarations that Christians are “infidels” who should be targeted in Egypt, this attack is also unlikely to be the last.

At the time of this writing, no one has yet taken responsibility for the attack. But ISIS is a likely suspect. There are quite a few militant groups in Egypt, but only one has a record of purposely targeting Christians in this deadly fashion, calling them their “favorite prey”—and that’s ISIS.

Against this backdrop, it’s difficult not to see this attack as having a deeply political purpose: to encourage the exodus of Christian Egyptians from their homeland. Through attacks like these, the perpetrators appear to be indicating that they don’t simply want to make life difficult for Christians—they want Egypt to be Christian-free. In a radical extremist vision for Egypt, it seems, there is no room for this ancient and rooted Egyptian community.

It’s not clear how successful radical extremists have been so far in this regard, because there are no reliable figures that take full account of Christian emigration from Egypt. But certainly, anecdotally, it would appear that Christians have left in far greater numbers over the last few years and that internal migration of Christians has also increased. Some within this group—one that has been protected in Egypt since the dawn of Christianity—now wonder whether this moment represents the dusk of their community in Egypt.

It would be comforting to think that this is purely about ISIS. And it’s true that ISIS is the main militant threat against Christians, and against wide swathes of other Egyptians more generally. ISIS doesn’t simply target Christians; ISIS targets Egyptians in Egypt, as it targets Iraqis in Iraq, and others in other countries.

But ISIS also feeds off a preexisting sectarianism that provides a certain type of background music for ISIS activities. Huge swathes of the Islamist camp in Egypt cannot claim to be putting forward a vision of genuine respect in the country, even though they may condemn Friday’s attack. In much of the pro-Islamist media, the Arabic-language discourse around Christians is clear, and clearly more negative than the discourse that appears in English-language media used for PR purposes with the West.

Sectarian incitement and anti-Christian populism are not limited to the ISIS cohorts and cells in Egypt. ISIS may take the sectarianism to an ultimate conclusion, but before ISIS ever existed in Egypt, a vile sectarianism had already infected far too much of the pro-Islamist universe. It has spread by playing to the baser, more populist sentiments among the pro-Islamist camp.

As Taylor Luck noted earlier this month in the Christian Science Monitor, Muslim antipathy toward Christians has been simmering for a long time, and has occasionally erupted into mob violence:

One of the largest waves of anti-Christian violence was after the 2013 military ouster of Islamist President Mohammad Morsi … and the army’s bloody crackdown against a sit-in by Muslim Brotherhood supporters in which nearly 1,000 Islamists were killed. Brotherhood officials singled out Copts, and particularly Coptic Pope Tawadros, for being complicit in the General Sisi-led military coup, and Christians were the target of angry supporters.

In August 2013, Human Rights Watch reported that mob violence led by Brotherhood supporters damaged 42 churches and dozens of schools and businesses owned by Copts across Egypt, killing several and trapping Christians in their homes.

Islamist circles and some Muslims across Egypt, meanwhile, use rhetoric deriding Christians as a “favored class” that is “hoarding wealth” and benefits from the regime, fault-lines that ISIS is looking to exploit.

We shouldn’t group all of the Islamist camp, whether in Egypt or otherwise, together with ISIS; that would be inaccurate. But at the same time, we have to acknowledge that ISIS thrives on sectarian background music that has long been provided by other parts of the Islamist universe, and not only by ISIS’s own media apparatus.

One of many ironies is that if nothing else, Friday’s appalling attack shows, yet again, how unorthodox groups like ISIS really are when it comes to Islam. In one of the many condemnations issued by Muslim religious figures and released today, one particular saying of the Prophet Muhammad’s, recorded in the hadith literature, stood out to me: “Whoever harms a person of the covenant [a non-Muslim in a Muslim territory], I am his adversary; and I will be his adversary on the Day of Judgement.” How much clearer can that be? And yet, those who seek violence will find hermeneutic ways to ignore this direct warning.

As ISIS continues to lose territory in Iraq and Syria, it will carry out or claim acts of terror elsewhere to bolster its public image. We’ve just seen an example in Manchester, and another in Indonesia, and regrettably there are likely to be more examples ahead. ISIS will disappear eventually. But if we want to shorten its shelf-life, taking the issue of sectarianism seriously is not a luxury, but a must.