Patrick Cockburn: The superpower deal on Syria is a plan for war as well as peace

There is a less obvious long-term reason why Assad may be happy to stop his air force attacking opposition areas and bombing civilian targets. The backbone of the non-IS armed opposition groups is Nusra, whose suicide bombers have led every successful rebel offensive. It is well organised, militarily experienced, fanatical and popular in the areas it controls. The Syrian political exiles and their sympathisers have always tried to mask the fact that these extreme Islamists dominate the armed opposition in Syria itself. The idea that there are “moderate” fighters available to replace them and fight Assad has always been a myth.

This is one of the weaknesses of the agreement. The Nusra leadership and its thousands of fighters, some of the toughest men on the planet, are meant to stand still while supposedly moderate fighters make themselves scarce and take refuge under a US-Russian air umbrella. It is much more likely that Nusra will take the offensive and seek to disrupt a ceasefire that is much against its interests. Some Nusra leaders will argue that, if their movement is going to be targeted like IS, then they might as well ally themselves with IS with whom they previously fought a bloody inter-jihadist civil war.

Will any of this bring the end of the Syrian conflict nearer? Syria is full of pessimists who think that the present ceasefire will evaporate like past abortive attempts to bring this horrific war to an end. But the cynics may well be wrong because the nature of the war here has changed over the past two years. It has become thoroughly internationalised since the US became militarily engaged in 2014 when it started air strikes to stop IS winning more victories after it had captured Mosul in Iraq. A year later Russia intervened with its air force to back up Assad as his army faltered under the assaults of Nusra and IS.

In the past there have been plenty of spoilers who torpedoed attempts at negotiations. But they may not be so willing to do so this time round. Support from the Turkish government was crucial for the armed opposition in Syria, because Turkey acted as a rear base through which passed weapons and foreign volunteers. But today Turkey is more interested in combating the Kurdish quasi-state in northern Syria than getting rid of Assad.

There is a peculiarity about the US-Russian agreement which makes it difficult to judge its chances of success. There are clearly side deals and understandings so some potential opponents of the deal will have been bought off by secret concessions. Why, for instance, were Damascus and Moscow so mute when Turkey invaded northern Syria last month if they had not been told previously that the extent of the Turkish advance would be limited. We are still a long way from a complete peace in Syria, but secret and open diplomacy rather than war have started to set the agenda.

The US and Russia will now co-ordinate air attacks on IS and Nusra but this is not going to be enough to eliminate either of these battered but powerful movements. Tactical air strikes work when they are called in by effective ground troops, as has been shown in Syria over the past 18 months when well-trained Syrian Kurdish infantry repeatedly defeated IS thanks to the massive fire power of the US Air Force.

The US and its allies will try to create a moderate armed opposition to replace Nusra and IS but it is unlikely that they will succeed. Previous attempts to do this have been laughably unsuccessful with vast expenditure producing only a handful of men. The extreme Islamists may be weakening in Syria and Iraq but they remain formidable opponents.

A US-Russian partnership is the only political and military combination that has the power to end the present war. But it is a fragile alliance of leaders and countries who do not trust each other; many in Washington object to doing business with their old Cold War rival. But none of these critics have put forward a feasible alternative policy for ending the war, so if this agreement does not work nothing else will.