THERE have been many cruel twists to Syria’s civil war. Yet even as it has evolved—from peaceful uprising into desperate armed revolt, then to sectarian bloodbath and more lately into a petri- dish for jihadists and a punchbag for foreign actors—there have been no decisive moments. For years the conflict has been locked in a grisly chess-game of sieges and stalemates, forcing out ever more refugees as a cast of combatants, none able to defeat their rivals, ravages the land.

Now President Vladimir Putin of Russia has slapped a powerful new piece on the board, deploying a strike force of up to 2,000 men backed by aircraft, armour and intelligence kit. The sudden move mightily strengthens Mr Putin’s ally, Syria’s brutal but increasingly beleaguered regime. But just how Russia intends to use its force remains unclear. Russian power could simply heighten and further complicate the fighting. Or it could provide a decisive tilt, militarily and perhaps diplomatically. It depends on how Mr Putin plays his game.

The government of President Bashar Assad represents just one side in a war that is multifaceted, with the country broken into segments held by Islamic State (IS), Syrian Kurds, and an assortment of mostly Islamist anti-regime militias. Yet although Mr Assad controls less than a quarter of Syria’s territory, this still contains the bulk of its remaining people. Despite generous aid from Iran and Russia, his regime has recently been losing ground. The Syrian army, which once fielded some 250,000 troops, has dwindled to fewer than 125,000 men backed up by local militias and Shia “volunteers”, including soldiers from Hizbullah, supplied by Iran. Its superior firepower and monopoly of the air—excepting the American-led coalition striking IS—has delayed but not deterred advances by the rebels, who may be weak and fissiparous but draw from the deep well of hatred felt by many Syrians, and especially the 70% who are Sunni Muslim, for a regime dominated by Mr Assad’s Alawite sect.

Best friends, but probably not forever Russia’s help comes in the nick of time. Mr Assad’s air force has been effective for bombing rebel-held areas, and so generating refugees. But its shrinking number of ageing aircraft are unable to provide close support in tactical combat. Enter Russia. The force now deployed to a coastal airbase in Syria’s Alawite heartland includes two dozen heavily armoured ground-attack jets as well as helicopters, possibly including Russia’s newest aerial battleship, the highly capable and lethal Ka-52. Russia has also supplied intelligence drones and signals equipment. Reports suggest that further deployments are likely soon, with satellite imagery showing expansion work at several Syrian bases along the coast, as well as at the port of Tartus, where Russia maintains a naval supply depot. Although Russian pilots are not known to have flown any combat missions yet, this configuration suggests they may soon do so. Such added clout could give Mr Assad a significant advantage on several battlefronts. On the Ghab plain in the west rebel forces have lately pushed south, threatening to cut Syria’s coast from the interior. In the desert to the east, IS this spring captured government-held oil- and gasfields as well as the ancient city of Palmyra, and is besieging a regime airbase outside the city of Deir al-Zor. But the jihadists’ supply lines are stretched and vulnerable to attack from the air. Added air power could also prove useful for strengthening the narrow corridor linking government-held parts of Aleppo, Syria’s second-largest city, with the south. “The entry of Russia could be a military game-changer on some fronts,” says Emile Hokayem of the International Institute for Strategic Studies. “But will it allow Assad to reassert full control? No.” Rather than a bid to end the war to the Syrian leader’s advantage, Russia’s move may be aimed at preventing his regime’s collapse. At the same time, say diplomats and analysts, Mr Putin wants to repair ties with the West, and to build leverage over vexed issues such as Ukraine, by posing as a potential partner in the fight against IS.

For Russian domestic opinion, Mr Putin has framed the deployment as a contribution to the war on Islamist terrorism, as a bolstering of Syria’s legitimate government, support for Syria’s Orthodox Christians and as a corrective to “childish” American policies that Russian media depict as having both fostered terrorism and failed to fight it . Russia has a particular concern, too, with what its intelligence service, the FSB, claims are 1,700 Russian jihadists, mostly Muslims from the Caucasus, who have joined Syrian rebel factions. Others say the number is almost twice that.

The Russian move has certainly left America and its allies looking flat-footed. Mr Putin’s boldness contrasts sharply with the timidity of Western efforts in Syria, which have wavered between lukewarm support for anti-Assad fighters and tacit collaboration with his regime in fighting IS. A recent series of embarrassments for the Obama administration, including the capture or defection of Syrian fighters vetted and trained in a costly Pentagon programme, as well as barbed comments from the White House attempting to disown its own policy, have not improved Western morale. And in any case the members of the American-led coalition, which has spent a year bashing IS in Syria from the air without much effect, remain divided by divergent aims and priorities.

Frustration with Syria’s chronically divided opposition and with Syria in general, as well as alarm in Europe at the surge in refugees pounding at its gates, have produced an increased willingness among Western diplomats to soften their hostility to Mr Assad’s regime. John Kerry, America’s secretary of state, said recently that, in a negotiated solution, the Syrian leader’s departure need not necessarily take place “on day one or month one or whatever”. America had previously firmly backed the demand by allies such as Turkey and Saudi Arabia that Mr Assad’s exit was a precondition for a deal.

Russia’s embrace of the Syrian leader has accelerated this shift. Senior European diplomats, including Germany’s foreign minister, Frank-Walter Steinmeier, welcome Russian intervention. Israel, which has kept a wary eye on neighbouring Syria, and in particular on Iran’s growing influence, is keener to co-operate with Mr Putin than to oppose him. Its prime minister, Binyamin Netanyahu, paid a friendly visit to Moscow, accompanied by top military brass, to seal protocols to ensure that there will be no unintended clashes between Israeli and Russian forces.

Even Turkey’s president, Recep Tayyip Erdogan, saw no problem flying to Moscow on September 23rd for the inauguration of a new mosque, claimed as the largest in Europe. The Pentagon, for its part, plans to make way for the new intruders in Syria’s crowded air space.

But the apparent pro-Moscow tilt has left many of Syria’s rebel factions seething. As a greater threat to Mr Assad than IS, they are more likely than the so-called caliphate to bear the brunt of an emboldened Syrian army’s attacks. At the same time, however, there are signs of a shift to more pragmatic politics among rebel groups. After months of complex negotiations involving Iran and one rebel coalition, agreement has been reached for a ceasefire and population swap in two besieged zones. In exchange for withdrawing rebel fighters from the town of Zabadani near the Lebanese border, and a limited cessation of government air attacks, the rebels will allow up to 10,000 villagers to leave a Shia enclave in the north.

Some 29 rebel factions also signed an agreement in Istanbul earlier this month endorsing a UN plan to set up four parallel working groups to seek practical solutions to Syria’s myriad woes. The plan represents a climb-down from previous, fruitless efforts to start peace negotiations. But the greater willingness of rebels to talk, combined with the painful ironing out of complex lines of engagement by deals such as the Zabadani ceasefire, suggests some room for movement: not yet towards an overall peace accord, but at least towards partial disengagement.

Mr Putin could play a positive role in this, if he chooses to use his power to nudge Mr Assad towards talks rather than goad him into battle. Western diplomats could help, too. Rather than scuttling aside to make way for Russia, they might instead use Mr Putin’s deeper and more dangerous exposure to extract concessions, such as an end to Mr Assad’s deadly barrel-bombing of civilians. But if Russia decides it can impose a military solution, it may be in for trouble. “This conflict has the fuel to last a few more years,” warns Mr Hokayem.

Correction: This article originally mischaracterised Russian forces as Soviet. We regret the error.