At the end of the eighth century, Harun al-Rashid, a caliph of the Abbasid dynasty, built a palace in Raqqa, on the Euphrates River, in what is now Syria. His empire stretched from modern Tunisia to Pakistan. It was an age of Islamic discovery in science, music, and art; Rashid’s court of viziers inspired stories in “One Thousand and One Nights.”

In June, the Islamic State in Iraq and al-Sham (ISIS) declared Raqqa the seat of a new caliphate, presided over by Abu Bakr al-Baghdadi, a fierce preacher who was once an American prisoner in Iraq, and is now in hiding. The city has lost its splendor. Public executions are “a common spectacle” on Fridays in El Naim Square or at the Al Sa’a roundabout, a United Nations human-rights commission reported last month. ISIS fighters mount the dead on crucifixes, “as a warning to local residents.”

ISIS emerged a decade ago as a small Iraqi affiliate of Al Qaeda, one that specialized in suicide bombings and inciting Iraq’s Sunni Muslim minority against the country’s Shiite majority. The network regenerated after 2011 amidst Iraq’s growing violence and the depravities of Syria’s civil war. This year,ISIS has conquered cities, oil fields, and swaths of territory in both Syria and Iraq. The movement draws its strength from Sunni Arab communities bitterly opposed to the Shiite-led government in Baghdad and the Alawite-dominated regime in Damascus, led by Bashar al-Assad.

Defense Secretary Chuck Hagel has called ISIS “as sophisticated and well funded as any group that we have seen . . . beyond anything we have seen.” The group has former military officers who can fly helicopters, spot artillery, and maneuver in battle. ISIS is increasingly a hybrid organization, on the model of Hezbollah—part terrorist network, part guerrilla army, part proto-state.

President Obama has decided that the United States must now attack ISIS, if only from the air. The President vacationed on Martha’s Vineyard, and golfed conspicuously, as his initial aerial campaign in Iraq unfolded. He has been less than forthright about why, after pledging to end America’s costly war in Iraq, he believed a return to battle there was necessary. But in interviews and other forums Obama has offered a casus belli, in three parts.

ISIS has massacred religious minorities, including Christians and Yazidis, and American air strikes can prevent more wanton killing, the President has said. A second imperative is the defense of the Kurdistan Regional Government, a semi-autonomous, oil-endowed American ally in northern Iraq, which a few weeks ago was teetering under pressure from ISIS but has since recovered, with the aid of American air power. The third, and most resonant, reason that the President has given is self-defense: to disrupt ISIS before it tries to attack Americans in the region or inside the United States.

ISIS has beheaded one American journalist, James Foley, and threatened to execute a second. Yet some terrorism specialists point out that ISIS is consumed by the sectarian wars in Syria and Iraq, and has shown no intent to launch attacks in the West, or any ability to do so. Still, ISIS has attracted five hundred British volunteers, many scores of other European passport holders, and even some Americans to its fight; they might eventually turn toward London, Berlin, or New York. Last week, British authorities announced that the threat of a terrorist attack on its home soil was “severe,” given the rising number of British jihadis now among the militants in Iraq and Syria.

The question about President Obama’s resumption of war in Iraq is not whether it can be justified but where it will lead. Air strikes against a well-resourced guerrilla army will do little if they are not accompanied by action on the ground. It would be a catastrophic error for the United States to take on that role. But what other professional force will dislodge the self-proclaimedISIS caliphate and then control the population? American policy assumes that Iraq’s squabbling politicians will rally a Shiite-led army to fight ISIS in the country’s Sunni heartland. On recent evidence, this assessment looks unrealistic.

In Syria, the options are worse. Obama has said repeatedly that he does not believe that Syria’s moderate rebels have the capacity to overthrow Assad or defeat jihadists. Yet the alternatives would allow Syria’s violence to fester at the cost of tens of thousands more civilian lives or would tacitly condone an alliance with the brutal Assad, who has been implicated in war crimes.

Obama and his advisers have at times taken refuge in a self-absolving logic: We can’t force people in other countries to unite around our agenda, so, if they don’t, whatever calamity unfolds is their responsibility. As a retreat from American hubris, this form of realism has appeal. As a contribution to a stable Middle East, it has failed utterly.

It is not yet clear that ISIS will endure as a menace. Fast-moving extremist conquerors sometimes have trouble holding their ground. ISIS has promised to govern as effectively as it intimidates, but its talent lies in extortion and ethnic cleansing, not in sanitation and job creation. It is vulnerable to revolt from within.

The group’s lightning rise is a symptom, however, of deeper instability; a cause of that instability is failed international policy in Iraq and Syria. If the United States is returning to war in the region, one might wish for a more considered vision than Whack-a-Mole against jihadists.

The restoration of human rights in the region first requires a renewed search for a tolerable—and, where possible, tolerant—path to stability. ISIS feasts above all on the suffering of Syria, and that appears to be unending. The war is in its fourth year, with almost two hundred thousand dead and nine million displaced, inside the country and out. The caliphate now seated in Raqqa is the sort of dark fantasy that can spring to life when people feel they are bereft of other plausible sources of security and justice.

“We don’t have a strategy yet,” the President remarked last week, infelicitously, about Syria. He does have a coalition of allies in the region that are willing to challenge ISIS’s ambition, including Jordan, Turkey, Saudi Arabia, and the United Arab Emirates. These countries patronize disenfranchised Sunnis in Iraq and Syria, and some of their support certainly reaches jihadists, includingISIS. Yet they share an interest in reducing Syria’s violence and in promoting regional and local Sunni self-governance that is less threatening and more sustainable than what ISIS has created. Ultimately, Sunnis will need the kind of autonomy that Kurds presently enjoy.

Leading a coalition of this character is hard, uncertain work. George H. W. Bush, the President whose foreign policy Obama seems to admire most, did it successfully in the runup to the Gulf War of 1991, by intensive personal engagement. Obama has more than two years left in the White House. To defeat ISIS, but also to reduce its source of strength, will require the President to risk his credibility on more than just air strikes.