The beheading of American journalist James Foley is only the latest in a catalogue of atrocities perpetrated by the Sunni militants of the Islamic State, also known as Isis. But Foley's murder and the grotesque video documenting it have finally shocked western capitals into grasping the threat that Isis represents far beyond the limits of the territory in Iraq and Syria now under its control. United States air power in support of Iraqi troops and Kurdish forces last week helped to recapture Mosul dam, a key infrastructural asset that had fallen into the hands of the militants. A few days earlier, US marines and special forces led the rescue of members of the Yazidi minority who were trapped on top of Mount Sinjar and afraid to leave because they would be murdered by Isis.
Such operations can help to degrade Isis militarily but they fail to address the group's most important strategic advantage, the fact that it operates in both Iraq and Syria. Gen Martin Dempsey, the top military figure in the US, acknowledged last week that Isis cannot be defeated without addressing "both sides of what is essentially at this point a nonexistent border". Although some in Washington are calling for US air strikes on Isis enclaves inside Syria, any such action would contravene international law unless it was approved by the Syrian government. Bashar al-Assad's government in Damascus, which appeared to tolerate the rise of Isis because of its destructive impact on other opposition groups, has now launched its own military crackdown on the jihadis.
President Barack Obama has been properly cautious about expanding the US military role in a region from which it withdrew in 2011, initially refusing to offer support to Iraqi forces until the polarising, sectarian prime minister Nouri al-Maliki stepped down. Maliki's successor, Haider al-Abadi, who was endorsed by both Tehran and Washington, has promised a more inclusive government that will give a stronger voice to Iraq's Sunni and Kurdish minorities. Unlike some of his critics, Mr Obama appears to understand that Isis cannot be defeated by military means alone but that the political grievances of the Sunnis in Iraq and in Syria must be addressed.
Throughout the region, governments that facilitated the expansion of Isis are waking up to its dangers. Iran and the US have shown they can co-operate when their mutual interests demand it and the threat of Isis should galvanise a broad coalition including the conservative Sunni Arab states. An essential step towards defeating the militants is to end the civil war in Syria, which has already claimed at least 191,000 lives. Instead of arming the Syrian opposition, as some US politicians are urging, the international community should reconvene the Geneva peace talks which ended in mutual recriminations earlier this year.