Russia’s return to the status of a great power has been obvious for some time. A Middle East leader who asked a senior American general earlier this summer about US plans for military intervention in Syria was told that prospects differed from the past because “Russia is back” as a major player.

The agreement reached by Russia and the US yesterday calling for Syria’s arsenal of chemical weapons to be removed or destroyed, represents the first time that Russia has been so centrally important on the international stage since the last days of the Soviet Union, when Moscow was marginalised in the months between the Iraqi invasion of Kuwait in 1990 and the US-led counter-attack in early 1991. I remember sitting with the Soviet chargé in the Al Rashid Hotel in Baghdad as he agonised over the fate of the Soviet Union, which preoccupied him far more than developments in Iraq.

Russia’s status in Syria as a crucial ally of President Bashar al-Assad is uniquely favourable to the Kremlin. It does not mean that Russia can dream of emulating the influence and power of the old Soviet Union. But it does demonstrate that Russia’s long retreat as a world power is coming to an end.

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Only two-and-a-half years ago, the US and Nato felt free to double-cross Moscow by using its naive assent to Western military intervention for limited humanitarian ends in Libya as if it was permission to overthrow Muammar Gaddafi.

For Russia, its Libyan debacle was the latest in a series of humiliations stretching back to the dissolution of the Soviet Union in December 1991. The US had assured the Kremlin that it would not expand its military alliances into Eastern Europe if Russian forces withdrew, but soon former members of the Warsaw Pact were joining Nato. In December 2001, President Bush withdrew the US from the Anti-Ballistic Missile Treaty which had been central to arms control for 30 years. Estonia, Latvia and Lithuania joined Nato.

What is different today is that the US is politically and militarily weaker than it was 10 years ago, because of its failure to win wars in Iraq and Afghanistan. The US position has been further undermined by a series of missteps in Syria, including the miscalculation that it would be as easy to get rid of Assad as Gaddafi. Washington and the West Europeans forgot that Gaddafi had only fallen because the Libyan rebels were backed by a full-scale Nato air campaign. Failing this, the Libyan rebels were never going to win on their own and the same is true in Syria.

US intentions in Syria are contradictory because Washington dislikes the opposition almost as much as the government. It fears that if Assad goes now he might be replaced by anarchic forces in which al-Qa’ida-linked militias would be a powerful if not predominant component. Washington’s attitude to Assad is like that of St Augustine towards sin: it would like to get rid of him but not quite yet, and certainly not until there is a force more sympathetic to the US capable of taking power in Damascus.

This dilemma may soon be out of date: the Assad government shows no sign of imploding. The al-Qa’ida-linked al-Nusra Front and the Islamic State of Iraq and the Levant are gaining in strength and are in the forefront of the fighting in close co-operation with the supposedly moderate Free Syrian Army. US Secretary of State John Kerry played down the influence of al-Qa’ida in Syria, leading Vladimir Putin to respond tartly: “He’s lying. And he knows he’s lying. It’s sad.”

Ideally, the US and its allies would like a coup within the Syrian government that would get rid of Assad and his family, but otherwise maintain the status quo. But Ba’athist regimes in Iraq and Syria were designed to be coup-proof: the intelligence services are too powerful and omnipresent for an anti-Assad plot to succeed. The rebels are probably relieved at this, as they do not want “Assadism without Assad”, just as, 10 years ago, the Iraqi opposition was nervous that the US occupation authorities post-invasion would opt for “Saddamism without Saddam”.

The Syrian civil war has so far produced many strange twists and turns and there may be more to come. Conventional wisdom had held that it was highly unlikely that the Syrian army would use poison gas because this would make US military intervention inevitable. The Russians and the Iranians still claim that the Syrian government would not have done something so self-destructive. But, amazingly, the crisis provoked by the use of chemical weapons in Damascus on 21 August has hitherto been to Assad’s advantage, because it has exposed the overwhelming unpopularity in the US, Britain and France of further military adventures in the Middle East. Previously, politicians had spoken of the legacy of failure in Afghanistan and Iraq, but they had grossly underestimated the strength of public hostility.

It is easy to overstate the extent to which the US is less of a power in the Middle East than 10 years ago. The implosion of Syria since 2011 is in its interests since, whoever wins the civil war, Syria will be weak, divided and no longer an obstacle to American influence. Moreover, no other power or combination of powers is in a position to take America’s place. When the US does not take the initiative in the region, nobody else does.

The Syrian rebels may sense that the game is slipping away from them. For all the US desire to keep the threat of air strikes against Assad in reserve, President Obama’s ability to order an attack is in practice limited by its unpopularity at home and the need for co-operation with Russia abroad. Agreement on eliminating Assad’s chemical weapons requires Assad’s co-operation. Chemical weapons have become the central focus of diplomacy rather than, as had previously been the case, Assad’s departure. Having successfully confronted and then conciliated the US over Syria, a resurgent Russia cannot see its protégé go down to defeat.