Many argue that ISIS is close to death. But whatever happens in Raqqa, ISIS’s cause will live on.

Three years after it emerged, the Islamic State is said to be on the road to defeat. In recent months, ISIS has suffered stinging reverses. This week, with its grip over Mosul being pried off by the Iraqi army, ISIS destroyed the al-Nuri mosque where Omar al-Baghdadi declared the caliphate in June 2014.

Across the border, its capital is under siege by the Syrian Democratic Forces (SDF) assisted by U.S. airpower. This progress in the war against ISIS should be a cause for celebration, but a modicum of caution is in order. For whatever the near-term outcome of the military campaign against ISIS, its cause will only be impaired, not extinguished, by defeat on the battlefield.

A leading reason for ISIS’s effective restoration of the caliphate has been its ideological and religious dimension, namely its core doctrines of martyrdom and jihad. This belligerent piety has been fastened to a frenzied triumphalism that awaits the worldwide victory of Islam. This tradition has incited what Maajid Nawaz has aptly termed a “global jihadist insurgency,” in evidence from London to Lahore, and it shows no sign of abating.

We Should Never Underestimate Evil

Those who doubt the potency of this ideology should remember that the rise of the Islamic State took much of the world by storm. In a 2014 interview with The New Yorker, President Obama infamously pronounced the blood-spattered theocratic gang to be no more than a “JV squad” (compared with the varsity squad, al-Qaeda) with limited capacity to fulfill its mad totalitarian vision.

Within the month, however, ISIS’s blitzkrieg sacked Falluja and would soon conquer fully a third of Iraq in addition to bulldozing its border with Syria. By June 2014, Iraq’s well-equipped but inept army abandoned Mosul, the country’s second largest city, in the face of the ISIS onslaught. The caliphate was born.

Many observers greeted this self-declared Islamic empire as a new enemy, and its control of a nation-state did indeed set it apart from its predecessors. It’s truer to say ISIS is an old enemy that became a new one. In their searching examination of the Islamic State, “ISIS: Inside the Army of Terror,” Michael Weiss and Hassan Hassan explain, “the United States has been at war with ISIS for the better part of a decade under its various incarnations” (i.e., al-Qaeda in Iraq). What happened to AQI is revealing because in the record of its undoing lies a plausible approach to defeating ISIS and keeping its successors at bay in the future.

From DOA to Major Terror Force

In 2007, the Bush administration ordered the “surge” to buttress the “Anbar awakening” that was challenging AQI for control of Iraq’s Sunni heartland. The effect of this change in strategy was astonishing. After years sewing sectarian strife with virtual impunity, AQI suddenly found its erstwhile patrons among the Sunni tribes had defected to the infidel. Deprived of their protected havens, AQI fighters swiftly became marked men. By 2010, AQI was “dead on its feet,” as terrorism expert Michael Knights told Congress.

Years later, as I have written before, two events resurrected this lifeless enemy. First, the Assad regime in Damascus incited civil war by crushing pro-democracy protests. The Syrian revolt devolved into a clash between Assad’s brutal mukhabarat state and ruthless, highly organized jihadist bands. Meanwhile, after the United States withdrew its military forces and diplomatic heft from Iraq, the Maliki regime reverted to the cruder instruments of sectarian rule. The corrupting effect of majority tyranny hollowed out the Iraqi army, which eventually ceded territory to a considerably smaller force of holy warriors fighting under the banner of ISIS.

As it passes its three-year mark, the scale of ISIS’s achievement leaves one gasping. The so-called caliphate was able to conquer wide swathes of territory and hold millions of people in bondage. Even after a robust American-led air campaign eliminated thousands of its fighters, ISIS boasted far more fighters (roughly 20,000) than al-Qaeda had at its peak. Even after it lost most of its territory in Iraq and Syria, ISIS has created and sustained functioning militias outside its homeland. ISIS “provinces” have been established in Libya, Egypt, Nigeria, Saudi Arabia, Yemen, and Afghanistan. More recently, it has made inroads into Southeast Asia.

ISIS’s state-building project has inspired a new generation of aspiring jihadists. Recruits have flocked to the Euphrates River Valley—at least 40,000 of them, by conservative estimates. Still more have undertaken their own franchises in anarchic lands or carried out “lone-wolf”—or, better put, “self-starter”—attacks on western soil.

ISIS Might Fade, But Its Causes Won’t Soon

For too long, the West has underestimated the threat of Islamic totalitarianism. The fact that ISIS does not pose an “existential threat” to the United States does not mean it cannot wreak havoc on the global order. A day before its agents slaughtered 130 people in Paris in November 2015, Obama boasted the Islamic State was “contained.” White House official Ben Rhodes then reassured Americans that “there’s no credible threat to the homeland at this time.”

This trite nonsense came after the Garland, Texas attack on a “draw Mohammed” contest and the Chattanooga shooting that killed four Marines and a Navy sailor. It was followed by the San Bernardino attack that killed 14 people, and Orlando, where 49 people were killed in a gay nightclub. If this grisly pattern is any indication, there is good reason to believe that the power of ISIS’s example will outlive it.

Even after the black flags have been furled in Raqqa, the conditions that birthed ISIS—the civil war in Syria and the sectarian regime in Baghdad, both of which inflamed the grievances of the alienated and abused Sunni population—will continue to fester. In Iraq, the failure to check Iran and its Shiite proxies have allowed ISIS to offer itself as the defender of last resort to an embattled Sunni minority. In Syria, the failure to depose Assad from power and prevent an ever-worsening vortex of violence constitutes America’s greatest foreign policy blunder of the decade.

A better strategy would act to secure legitimacy in the Sunni heartland of Iraq and Syria lest victories against ISIS prove transient. Although this may entail more “boots on the ground,” this seems a moot point when Obama—no champion of U.S. military power—dispatched more than 4,000 soldiers to Iraq and numerous Special Forces units to Syria. Under President Trump, the United States has taken a number of measures, including airstrikes against Iranian UAV’s and Iranian-backed Shiite militias, designed to keep forces loyal to Assad on their heels.

The jihadist scourge across the Middle East is, to borrow from St. Augustine, so old and so new. For all of its technological savvy and pornographic savagery, ISIS represents a familiar foe, one we have successfully defeated before and may well defeat again. Yet without an ambitious American strategy to initiate a political settlement in Syria and Iraq backed by international force and legitimacy, the sources of ISIS will still be present even after the jihadist army is vanquished in Raqqa.