LONDON — Almost 13 years after 9/11,a jihadi organization with a murderous anti-Western ideology controls territory in Iraq and Syria, which are closer to Europe and the United States than Afghanistan is. It commands resources and camps and even a Syrian military base. It spreads its propaganda through social media. It has set the West on edge through the recorded beheading of the American journalist James Foley — with the promise of more to come.

What went wrong? The United States and its allies did not go to war to eradicate AlQaeda camps in Afghanistan only to face— after the expenditure of so much blood and treasure — a more proximate terrorist threat with a Qaeda-like ideology. The“war on terror,” it seems, produced only a metastasized variety of terror.

More than 500, and perhaps as many as 800, British Muslims have headed for Syria and Iraq to enlist in the jihadi ranks. In France, that number stands at about 900. Two adolescent girls, 15 and17, were detained last week in Paris and face charges of conspiring with a terrorist organization. The ideological appeal of the likes of the Islamic State in Iraq and Syria is intact. It may be increasing, despite efforts to build an interfaith dialogue, reach out to moderate Islam, and pre-empt radicalization.

“One minute you are trying to pay bills, the next you’re running around Syria with a machine gun,” said Ghaffar Hussain, the managing director of the Quilliam Foundation, a British research group that seeks to tackle religious extremism. “Many young British Muslims are confused about their identity, and they buy into an arrow framework that can explain events. Jihadists hand them a simplistic narrative of good versus evil. They give them camaraderie and certainty. ISIS makes them feel part of a grand struggle.”

A large part of Western failure has been the inability to counter the attraction of such extremism. Perhaps racked with historical guilt, European nations with populations from former colonies often seem unable to celebrate their values of freedom, democracy and the rule of law.

Meanwhile, in the Arab world the central hope of the Arab Spring has been dashed: that more open and representative societies would reduce the frustration that leads to extremism.

President Obama shunned the phrase“war on terror” to distance himself from the policies of President George W. Bush. But in reality he chose to pursue the struggle by other military means. He stepped up drone attacks on several fronts. His most conspicuous success was the killing of Osama bin Laden in 2011.

The curtain, it seemed, had fallen on America’s post-9/11 trauma. Then, a little over three years after Bin Laden’s death, ISIS overran the Iraqi city of Mosul and the world woke up to the radicalization through the festering Syrian war of another generation of Muslims; youths drawn to the slaughter of infidels (as well as Shiite Muslims) and the far-fetched notion of recreating an Islamic caliphate under Shariah law. When a hooded ISIS henchman with a British accent beheaded Foley last week, the new threat acquired urgency at last.

The list of American errors is long: Bush’s ill-conceived and bungled war in Iraq; a failure to deal with the fact that two allies, Saudi Arabia and Pakistan, have been major sources and funders of violent Sunni extremism; an inability to seize opportunity in Egypt, home to nearly a quarter of the world’s Arabs, and so demonstrate that Arab societies can evolve out of the radicalizing confrontation of dictatorship and Islamism; a prolonged spate of dithering over the Syrian war during which Obama declared three years ago that “the time has come for President Assad to step aside” without having any plan to achieve that; a lack of resolve in Syria that saw Obama set a red line on the use of chemical weapons only to back away from military force when chemical weapons were used; an inability to seethat no one loves an Arab vacuum likejihadi extremists, and a bloody vacuum was precisely what Obama allowed Syria to become; and inattention, until it was too late, to festering sectarian conflict in a broken Iraqi society left to its fate by a complete American withdrawal.

The chicken that came home to roost from the Syrian debacle is called ISIS. It is not Al Qaeda. But, as the journalist Patrick Cockburn has noted, Al Qaeda “is an idea rather than an organization, and this has long been the case.”

ISIS grew through American weakness— the setting of objectives and red lines in Syria that proved vacuous. But the deepest American and Western defeat has been ideological. As Hussain said,“If you don’t have a concerted strategy to undermine their narrative, their values, their worldview, you are not going to succeed. Everyone in society has to take on the challenge.”