Iraq's dismal choices: At a time when none of the options looks good, it may just be a question of trying to avert the worst scenario

The outside world cannot hope to reverse the course of events in Iraq by intervening

It will be some comfort to America and its allies, as well as to most Iraqis, that Iraq's ramshackle armed forces appear to have stalled the march on the capital by the Sunni jihadists. The fall of Baghdad to the fighters of Isis would be a catastrophe of epic proportions, virtually terminating Iraq's existence as a state. It would also give the jihadists and their putative caliphate a real capital, and force millions of Iraqi Shia to flee from their homes. It is hard to imagine the Middle East absorbing the shock.

That apocalyptic scenario has been averted, if only for the meantime, and the Middle East and the wider world can exhale - just. Nevertheless, even if Iraqi forces succeed in containing the Isis fighters about 60 miles north of Baghdad, the long-term prognosis for the country and its neighbours remains desperately worrying.

If - as seems more than likely - Isis retains much of north and north-west Iraq, possibly ceding the odd frontline town back to Iraqi forces, it will still be possession of a de facto state composed of large, contiguous chunks of Iraq and Syria. In that case, the boundaries that the British and French imposed on the Middle East after the First World War will have ceased to exist. Iraq and Syria will share the dismal fate of Somalia in the Horn of Africa, becoming failed, former states; vacuums on the map of the world, drawing in - and expelling - all sorts of destabilising energies.

It is true that the frontiers of Iraq and Syria were drawn arbitrarily to reflect the temporary interests of British and French colonialists. Perhaps both countries - like that other notable post-Versailles creation, Yugoslavia - were viable only as military dictatorships, in which case nothing can be done to stop them from dissolving in the long term, or stop their embittered and hopelessly alienated Sunnis from creating their own entity out of the debris.

One problem is that these countries are unravelling in a completely uncontrolled fashion. Another is that the men of Isis have no intention of confining themselves to a medium-sized state based in north-west Iraq and north-east Syria. They are religious imperialists, and their fierce ideology teaches them that they must expand or die; if they consolidate control over their existing territories, they will soon turn elsewhere. The ethnically and politically fractured kingdom of Jordan is an obvious candidate for their malevolent attention.

The outside world, starting with the United States, cannot hope to reverse the course of events in Iraq by intervening on the ground, and President Barack Obama was right to rule out US troops going back there.

However, that doesn't mean taking up an observer's seat as the region descends into ever greater chaos. Washington should encourage the tentative rapprochement between Sunni Saudi Arabia and Shia Iran, both of which are starting to see just how dangerous the Sunni-Shia power struggle is becoming to each of them. We should do our utmost to shore up the defences of vulnerable but still stable states in the region, such as Jordan.

Western countries could also afford to be more generous in helping to address the humanitarian aspect of the latest crisis. Britain has so far offered an extra £3m to help tens of thousands of refugees fleeing the advance of Isis, most of whom are now camping in Kurdish-controlled areas of northern Iraq. It hardly seems an adequate gesture.

With any luck, the Sunnis in Syria and Iraq will at some point turn against their self-styled deliverers in Isis. In that case, it is vital that the Shia-dominated regime in Baghdad comes under pressure to keep the door open to talks about some kind of federal option for the Sunnis, and for the Kurds. It is late in the day for Iraq even to try to play with the federalisation option, but just possibly some kind of gossamer-thin state can be salvaged from the current mess. Right now, none of the options looks good, but despair is not the answer.