In the early days after 9/11 there was a lot of talk about a “clash of civilizations” and a long “existential struggle” facing the West. I once asked the late Christopher Hitchens what he felt on that terrible day, and he said he felt no small amount of joy. Not for the suffering and death, but for the fact that the West finally had been awakened to the terrible but necessary struggle before us.

And for a time, many liberals bought into the idea that America was heading into a generational struggle with jihadism. There were a slew of books on the subject. Peter Beinart, for instance, wrote The Good Fight: Why Liberals — and Only Liberals — Can Win the War on Terror and Make America Great Again. As the subtitle suggests, there was a lot of partisan mischief in his argument, but it rested on the premise that liberals must accept that “Islamic totalitarianism” — his phrase — has replaced communism as our enemy.

On this, at least, Beinart and company, briefly agreed with George W. Bush that the war against “Islamic fascists” (Bush’s term) was the “decisive ideological struggle of the 21st century.” One jayvee squad — the self-styled Islamic State formerly known as the Islamic State of Iraq and Syria, or ISIS — now controls the territorial equivalent of Britain and is one of the best-equipped and ideologically committed military forces in the Middle East. Everyday jihadis — many with Western passports — enlist in the struggle to create a global caliphate while the “Muslim street” from Turkey to Saudi Arabia follows the Islamic State like a sports team.

The Islamic State’s atrocities are too numerous and too horrible to list here. It includes rape and slavery, religious cleansing, mass murder, public crucifixions, and beheadings. Over the weekend, an Iraqi official said that the Islamic State had killed at least 500 Iraqi Yazidis, burying some alive, including women and children. The group is only too happy to tweet about all of it.