It is just over a year since the Syrian regime lobbed chemical weapons into the suburbs of its own capital city, killing up to 1,500 in just a few hours in the early morning of 21 August. The victims are a small fraction of the estimated 192,000 Syrians (according to the latest UN figures) killed in the conflict since the spring of 2011. (Other estimates suggest the total figure could be well over 300,000.)

It is two years since Barack Obama’s statement on 20 August 2012 that “a red line for us is [if] we start seeing a whole bunch of chemical weapons moving around or being utilised”. When the Syrian regime openly flouted those red lines 12 months later, it seemed inevitable that the reluctant president would be forced into military action against Bashar al-Assad.

Ironically, it was Secretary of State John Kerry – a stronger advocate of air strikes than Obama – who let the regime off the hook when asked if Assad could do anything to prevent US action. “Sure. He could turn over every single bit of his chemical weapons to the international community in the next week,” he said, waving his arms exasperatedly. “But he isn’t about to do it and it can’t be done, obviously.” The Assad regime – with the assistance of the Russian foreign ministry – had just been handed the script to follow if it wanted to avoid outside intervention. As the chemical weapons were handed over, it escalated its campaign with conventional weaponry.

Another year on, we are in a new phase entirely. The fleet-footed rise of Isis has transformed how the conflict is viewed from the outside. It is said that the pre-eminence of militant jihadists in anti-regime Syria now proves there was no “moderate” opposition to support in the early stages of the uprising. But rather than being major participants in the civil war, Isis benefited from the unchecked strength of Assad’s assault against other rebel groups in the second half of 2013. Its strategy from the start was to establish its own supremacy (in the form of its putative caliphate) in areas where the regime has ceded control, and in areas of Iraq where the Baghdad government had lost all authority.

The idea that rapprochement with Assad is the route to defeating Isis is misleading. Assad has a long history of co-operation with the forebears of Isis, al-Qaeda in Iraq, having giving them complete freedom of movement over the border into Iraq to fight the insurgency against coalition forces there after the invasion in 2003. Those networks are the lifeblood of Isis to this day. In March 2011, as Assad began his clampdown on opposition activists, he also emptied the cells of the infamous Sednaya Prison outside Damascus, which was full of jihadists – many of whom are now playing leading roles in Isis. There are even some claims that the American photographer James Foley had been held by the Syrian regime before he made his way into the hands of Isis. For the moment, Isis and Assad are using each other for mutual benefit.

The murder of Foley and the plight of the Yazidis in Iraq are not only human tragedies but symbols of a loss of gravity in the international arena. What we are witnessing is the steady erosion of the post-cold war international order. The chief reason for this is that the US, which has borne by far the heaviest burden in maintaining this order (with all its flaws), has lost its desire to be the world’s policeman, a view articulated in Obama’s speech at the West Point Military Academy in May this year. It has understandable reasons for doing so, from a decade of bad experiences in the Middle East to internal problems such as immigration, and helped by increasing energy independence (perhaps the biggest “game-changer” of all).

In areas where America is less willing to flex its muscles – eastern Europe, the eastern Mediterranean and the Gulf region – the consequences are apparent. Before the crisis involving the Yazidis in early August, it was not American or British but Syrian, Iranian and Russian fighter planes that were operating in Iraqi airspace at the request of Baghdad. In the past week, without the knowledge of the US, Egypt and the United Arab Emirates launched air strikes against Islamist militias in Libya. Yet more Russian military operatives have just been picked up in Ukraine.

Horrific as it was, the beheading of James Foley will not change that calculus in Washington. It does have direct implications for British foreign policy, however. That Foley was killed by a jihadi with a London accent puts the problem in stark relief. The presence of hundreds of British citizens within the ranks of Isis is one of the gravest threats to national security for many years. Like it or not, a world in which Syria and Iraq disintegrate is a dangerous one for Britain. The risk is acute in London, from where most of the British fighters hail – as Boris Johnson’s posturing demonstrates.

For the past two centuries, British foreign policy has been predicated on the preservation of international order (one built, of course, for its own ends). It is when that order has collapsed that the gravest threats to British national security have occurred: in the 1910s and 1930s. The US can afford to turn inwards, as it has done periodically throughout the past century, but Britain has more immediate interests at stake in the conflict in Syria, just as it did in Libya (when the US was momentarily willing to “lead from behind”). There are severe limits to what the UK can do as a middle-ranking power. But it can do better than firefighting every crisis with an emergency meeting of Cobra. It needs a grand strategy to reflect two interrelated truths: that Britain has a selfish interest in striving to preserve the international order; and that the task becomes more difficult when its most important ally is less willing to do all the heavy lifting. 

John Bew is an NS contributing writer