The timeline of Syria’s grinding civil war is dotted with illusory turning points. These were atrocities or grim milestones that the world assumed would usher the conflict towards an endgame but served only to reinforce its horrendous, unswerving trajectory. The use of chemical weapons was one. The advance of Islamic State was another.

The pattern has held with almost every town that has fallen (Raqqa, Palmyra) or been razed (Aleppo, Homs), and with each new intervention by a foreign power. None has been decisive.

Instead the dynamic of the conflict has held firm. Four and a half years after it began amid the optimism of the Arab Spring, the war's aftershocks are still pulsing outwards, across the Middle East and into Europe, and the outside world is steadily and with varying degrees of reluctance being drawn further in.

0 of 3

The figures are staggering. Almost 250,000 Syrians, including nearly 12,000 children, have been killed since the conflict broke out, in March 2011, according to the Syrian Observatory for Human Rights, a UK-based activist group.

The economy has collapsed, and 80 per cent of the population lives below the poverty line. The United Nations estimates that more than 6.5 million have become internally displaced and a further 4.5 million – one in five of the population – have fled the country altogether, an exodus that has seen Syria overtake Afghanistan as the biggest source of refugees in the world.

The upheaval has been felt across the region. Having drawn tens of thousands of foreign recruits, Islamic State has swept east from its Syrian base to lay claim to a swathe of northwestern Iraq, allowing it to exercise brutal authority over an area that is home to 10 million people.

The vast majority of Syria's refugees have crossed into neighbouring Turkey, Jordan and Lebanon, where many of them subsist on handouts in sprawling border camps. One in four people in Lebanon today is Syrian.

The conflict itself rages on with no diplomatic solution in sight. Having begun when largely peaceful protests were violently suppressed by the government of Bashar al-Assad, Syria’s president, in March 2011, the war has metastasised to a point where the map of Syria is today carved into dozens of fiefs controlled by regime forces and an array of fragmented opposition factions. Each has its own aims and interests, but none is capable of taking enough territory to win the war or enforce a peace.

Assad retains control of the capital, Damascus, along with his strongholds on the Mediterranean coast. Jaish al-Fatah (the Army of Conquest), a loose alliance of armed rebel groups formed in March, has had significant victories in eastern Syria, notably in Idlib, a provincial capital, and in Latakia province, the heartland of Assad's Alawite sect.

The alliance, which includes Islamist factions such as the al-Qaeda-affiliated Nusra Front and Ahrar al-Sham, as well as more moderate groups, poses the greatest battlefield threat to Assad, and areas under its control have taken the brunt of Syrian-regime bombing.

In the northeast, Kurdish militias have made gains along the Turkish border; in eastern Syria Islamic State is tightening its grip while maintaining a corridor to Turkey’s porous border – a vital route for fighters and supplies.

Regional powers

In the background, meanwhile, regional powers jostle and manoeuvre to advance their own interests.

Saudi Arabia

,

Qatar

and other Persian Gulf states channel money and arms to Sunni rebels fighting the Assad government while taking part in or facilitating the US-led air campaign against Islamic State in the east.

Iran, implacably opposed to Sunni gains at Assad's expense, is the Syrian regime's staunchest ally. It has been providing military support, logistical assistance and funding since the start of the war, in 2011. Iran's Lebanese proxy, Hezbollah, joined the war on the government side in 2012 and has dug in at various points along the Lebanon-Syria border.

Turkey has allowed the American-led coalition to use its air bases, but the flow of fighters and supplies across its border with Syria has been a vital supply route for the opposition militants’ war effort.

Ankara is preoccupied, above all, with the Kurdish groups active just south of its border; the Kurds’ efforts to test how far they can expand their semi-autonomous zone in northern Syria have been met with Turkish bombardment from the air.

As a former US official told the International Crisis Group for a report in 2013, what once was a Syrian conflict with regional spillover has become a regional war with a Syrian focus.

Yet it's the intentions of two more distant powers – the United States and Russia – that have this week raised new questions about the direction of the war and the prospects for a political solution.

Russia has long supplied arms to Syria – its closest ally in the Middle East for decades – and has consistently extolled Assad as a bulwark against the Islamist insurgency. But Moscow upped the ante on Wednesday when, having given the US just an hour's notice, it carried out its first air strikes against anti-Assad forces in different parts of Syria.

President Vladimir Putin said Russia's objective was to prevent terrorist attacks at home by returning Islamic State militants (2,000 or more Russian-speakers are believed to be fighting against Assad's forces), but reports that Russian bombs fell on areas known not to have an Islamic State presence fuelled western suspicions that Putin had entered the fray mainly to head off any threat to Assad's rule.

For the Syrian army, Moscow’s intervention was a much-needed boost. It has been in retreat on several fronts since February this year, and Assad recently admitted that he badly needed more soldiers.

The US said in July that it was making contingency plans for the government’s sudden collapse or retreat from Damascus.

Global player

Putin, alive to the opportunity to burnish his credentials as a global player and mindful of the importance of Russia’s naval station at the Syrian port city of

Tartus

, its only remaining overseas military base outside the former

Soviet Union

, probably felt the need to “bolster the regime” at its moment of weakness, says

Yezid Sayigh

of the Carnegie Middle East Centre in Beirut.

“The Russians have always been primarily concerned with the state of the Syrian regular army. They’re especially keen that that state institution be preserved, whatever else changes in Syria. It’s the one that they’ve got the longest relationship with and that they’ve continued to support and buttress.”

But the intervention was also intended to send a message to Russia’s rivals for influence in Syria. “An immediate target, I think, has been to say to the Turks, who are talking of moving across the border to set up a safe zone, and to the Americans and the Saudis and others who have been involved in supporting the armed opposition, that ‘we are not going to allow more ambitious external involvement directly on the ground in Syria’,” Sayigh says.

Whatever the reason, he says, Moscow’s offensive is a “game changer” that pushes the conflict into unknown territory.

Fabrice Balanche, a political geographer and Syria specialist from the University of Lyons, predicts that Russian air strikes will focus on the area around Aleppo, Syria's largest city, where Assad's forces are under huge pressure. Government soldiers retain parts of the city centre, but opposition groups are on three sides.

At present the only route between Aleppo and the government zone is a small road through the desert. "Syria was born in the 1920s through the unification of the provinces of Damascus and Aleppo. So for Assad to lose Aleppo would be symbolically and strategically unthinkable," says Balanche, who is currently visiting fellow at the Washington Institute of Near East Studies.

Balanche believes Moscow has entered Syria “to hit not just Daesh [Islamic State] but all groups it regards as terrorists, including those supported by the Gulf monarchies and Turkey”.

Russia’s offensive coincides with a shift in the West’s position on Syria’s future. Since the war began the US and European capitals have agreed that Assad would have to step down or be removed for the conflict to end.

Recent signals from Washington are more nuanced. While President Barack Obama continues to insist that the Syrian president, whom he described at the UN General Assembly last week as a tyrant who drops barrel bombs to massacre innocent civilians, cannot have a role in the country's future, the Americans are now willing to accept that he may stay on for the duration of a political transition.

The rhetoric in other western capitals (if not in France, which is carrying out its own anti-Islamic State raids and remains implacably opposed to Assad staying on) has shifted along similar lines.

This reflects a growing sense that military pressure may not necessarily topple the regime or cause it to crack from the inside, as originally believed – at least not while Iran, Hezbollah and Russia remain determined to keep Assad in place.

Advocates for allowing Assad to stay on during the transition also argue that his early departure could run the risk of a chaotic collapse of state institutions.

Given that western powers cannot countenance a costly ground intervention of their own or accept an outright regime victory, that leaves a negotiated compromise – probably one brokered by each side’s external sponsors – as the most likely way to end the conflict.

On one reading Putin may even be anticipating this. In June he indicated Russia’s willingness to work with Assad “to ensure political transformation, so that all Syrians have access to the instruments of power”. Russia has no wish to get bogged down in an attritional war without end, says Balanche; rather “Putin wants negotiations in Syria but he knows that for negotiations Assad needs to be strong”.

Political transition

A diplomatic deal remains a long way off, however. Assad has given few indications that he is genuinely willing to cede power, while the fractious opposition is unlikely to accept any deal that would leave him in place.

Serious discussions have yet to begin among the main external players – the United States, Russia, Iran, Saudi Arabia and others – on the concrete shape of a political transition. Questions such as who would run the army, the police or the central bank, for example, have scarcely been broached.

Added to that is the war economy itself, which allows many players, including the regime and many opposition groups, to survive by being in a state of armed conflict.

“The one thing that might finally come out of the current developments is not a political deal but maybe an armed truce . . . where you might have an agreement to end aerial bombardment or hostilities, no further forward movement on the ground or exchange of territory, and start bringing in aid and economic activity,” says Sayigh.

“That could happen, but the chances are low, partly because very few players actually have an interest in a cessation of fire. They’ve got too much at stake.”

Outside influences: Where do they stand?

United States:

supports and trains moderate rebels, leads a military coalition waging an air campaign against Islamic State and other Islamist factions.

Russia: staunchly loyal to the Syrian president, Bashar al-Assad, Moscow this week began its own airstrikes against Islamist groups and other anti-Assad elements.

Iran: a close Assad ally, Tehran opposes Sunni insurgents, including Islamic State, and has played a key role in arming and funding the Syrian regime directly and through its Lebanese proxy, Hezbollah.

Saudi Arabia: a significant backer of Sunni rebel groups fighting against Assad, Saudi Arabia has also joined the US-led coalition against Islamic State.

Qatar: provides money, training and weapons to anti-Assad forces and allows the US to use one of its airbases as headquarters for the anti-Islamic State campaign.

Turkey: supports the US-led coalition, but its largely porous border with Syria has been a vital supply line for Sunni insurgents. Turkey's focus is on the Kurdish militias whose strength in northern Syria it aims to contain.