President Obama has just convened a conference on “Countering Violent Extremism,” his preferred euphemism for Islamist terrorism. His call for confronting “squarely and honestly the twisted ideologies that these terrorist groups use to incite people to violence” was good enough as far as it went–although it would have been more compelling if he himself would be willing to utter the word “Islam” in connection with the terrorist threat.

The president was right to say, “We need to find new ways to amplify the voices of peace and tolerance and inclusion.” But what he neglected to do entirely was to mention the most important way to counter the violent message of what is now the world’s most successful (and most threatening) terrorist group, the Islamic State of Iraq and Syria.

In the new issue of The Atlantic, Graeme Wood offers a long and invaluable analysis of what it is that ISIS wants and how to counter it. In the first place, he refutes the canard, popularized in good faith by President Obama, that ISIS is somehow “un-Islamic.” In point of fact, as Wood notes, ISIS leaders “insist that they will not—cannot—waver from governing precepts that were embedded in Islam by the Prophet Muhammad and his earliest followers. They often speak in codes and allusions that sound odd or old-fashioned to non-Muslims, but refer to specific traditions and texts of early Islam.”

There is no doubt that, mercifully, ISIS’s is a minority reading of Islam but that does not change the fact that its ideology is rooted in Islam and has legitimacy among some Muslims. A refusal to confront that reality will not help us defeat ISIS.

What will help defeat ISIS? Wood makes an important point here:

One way to un-cast the Islamic State’s spell over its adherents would be to overpower it militarily and occupy the parts of Syria and Iraq now under caliphate rule. Al‑Qaeda is ineradicable because it can survive, cockroach-like, by going underground. The Islamic State cannot. If it loses its grip on its territory in Syria and Iraq, it will cease to be a caliphate. Caliphates cannot exist as underground movements, because territorial authority is a requirement: take away its command of territory, and all those oaths of allegiance are no longer binding.

In short, if we can roll back ISIS’s territorial control, we will dissipate its appeal. How we can do that is subject to debate. Wood himself writes that suggestions from some analysts, such as Fred Kagan and me, to deploy tens of thousands of troops to fight ISIS are misguided and will backfire. He writes: “Given everything we know about the Islamic State, continuing to slowly bleed it, through air strikes and proxy warfare, appears the best of bad military options.”

And yet many months of those air strikes have failed to dislodge ISIS from the vast majority of its territory in Syria and Iraq–which, as Wood notes, is the only way to defeat this evil organization. At best those air strikes have blunted ISIS’ momentum in Iraq. In Syria they have not done even that much: ISIS has continued to expand its territorial control even while being bombed. This means, as Wood writes, that “an avowedly genocidal organization is on its potential victims’ front lawn, and it is committing daily atrocities in the territory it already controls.”

Wood is compelling in analyzing the ISIS threat–less so in suggesting a solution. His work points to the imperative for the US to do more to deny ISIS territorial control. That is why I have suggested the new for more than 10,000 US personnel to be deployed, primarily in an advise and assist capacity, so as to galvanize opposition to ISIS primarily among Sunnis in Iraq and Syria. Yes, this carries risks–but so does allowing ISIS to continue expanding, not only in the Levant, but also as far afield as Libya and Afghanistan.