US Secretary of State John Kerry believes that Friday 29 October's talks in Vienna are the best chance yet for an end to Syria's brutal four-and-a-half-year civil war, not least because they bring together bitter rivals Saudi Arabia and Iran, who have backed opposing sides in a conflict that has left over 250,000 people dead.
Saudi Arabia has opposed Iran's invite to the summit and it isn't difficult to see why. Riyadh and Tehran are currently fighting two proxy wars in the Middle East – the first in Syria and the second in Yemen, where Saudi Arabia is heading a pan-Sunni coalition against the Iranian-backed Houthi rebels from the north of the country.
But while Kerry's public optimism is to be expected, gaining any tangible solution to the Syria crisis from the talks will be a tall order. Not only are Saudi Arabia, Iran, Russia, the US and various European powers all currently backing various sides both militarily and diplomatically, but not a single Syrian party to the conflict has been invited to Vienna. While world leaders debate theoretical solutions, the guns will not be silent on the ground.
Indeed, the best top line to emerge from the Vienna talks will be a commitment on the part of all the foreign parties involved in Syria's civil war to work towards finding a lasting solution. In the context of Syria, where the international community has consistently failed to formulate a coherent strategy for the ending the crisis for almost five bloody years, a deal to work towards a further deal is no mean feat.
"There is almost no hope of a tangible agreement coming out of these talks. The only positive might be a respective commitment to continue probing and engage in an ongoing dialogue that might, a long way down the road, lead to positive results," said Julien Barnes-Dacey, a Syria analyst at the European Council on Foreign Relations (ECFR).
The Middle East players in the conflict already have their cards firmly on the table. Iran's backing for Bashar al-Assad has looked even more solid since Russia intervened in the conflict. Hezbollah – the Iranian proxy based in Lebanon – fights alongside Assad's army against the rebels of the Islamic Front and Jabat al-Nusra, supported by the Sunni Muslim states of the Gulf, Saudi Arabia included.
Meanwhile, the US and European stance in the Syrian conflict is as confused as ever. The spectacular failure of US efforts to fund and train a third rebel force that could fight both Islamic State (Isis) and Assad was demonstrated in recent weeks when it was revealed that all but a handful of the fighters had either been captured or defected to al-Qaeda-affiliated Nusra Front.
US military action has focused on neighbouring Iraq, rather than Syria, where Washington and its European allies have struggled to find a party to the conflict that the public could stomach supporting. It may be simplistic to refer to Nusra as al-Qaeda given the evolution of the movement over the course of the Syrian conflict, but it would be naïve to deny the extremist Islamist element behind much of the opposition to Assad.
As for the Saudis, Foreign Minister Adel al-Jubeir has been open about Riyadh's intention of using the talks to illustrate that Iran's refusal to accept a Syria without Assad means that Tehran can never be a viable player in the peace process. Riyadh vehemently opposed the P5 + 1 nuclear deal between Iran and the West – as well as the gradual rehabilitation of the Islamic Republic on the world stage – and will hope it shows its true colours.
It is the question of Assad that will likely produce the deadlock in Vienna. Russia and Iran are intent on the dictator remaining in some sort of position of power after the conflict, which is a position that, even if the US and Europe were to grudgingly accept it, Turkey, Qatar and Saudi Arabia would not tolerate it. Indeed, one of al-Jubeir's only comments on the talks have been that they seek: "The time and means of Bashar al-Assad's exit".
Given those complexities, it is not a surprise that Syrian parties in the conflict have not been invited to Vienna. Nusra's extremist elements will always make it an unpalatable ally to the West, while what is often dubbed "the mainstream opposition" – meaning the Free Syrian Army and a dwindling handful of secular, Western-based dissidents – are weak, if not irrelevant, given the realities on the ground.
Who are the rebel groups fighting in Syria?
Check out the IBTimes UK guide to the militia groups fighting in Syria and their backers here.
"There is almost no chance that Syrians will be able to agree on anything at the moment, particularly as long as their respective regional backers continue to drive them in different directions. Syrian actors will have to be brought into the process but I think the logic as a first step to getting regional alignments," said Barnes-Darcy.
In a perfect world, the parties in Vienna could persuade Russia and Iran to focus its attention on IS with its airstrikes rather than on Nusra and the Sunni-backed anti-Assad militias, who could in turn be persuaded through their proxies to come to a series of local ceasefires with Assad's forces. That may at least halt the fighting in Syria in the short term and allow all parties to focus on IS and liberating cities such as Raqqa.
Longer term, perhaps Iran and Russia could be persuaded to drop their stubborn allegiance to Assad, and a federal Syria rid of IS could hold elections that would give both its Shia minority and Sunni majority fair representation. Saudi and its Sunni allies could be persuaded to be more discerning when funding Sunni militias with extremist tendencies and the West could gradually restore its shattered relationship with the Arab world.
But this is not a perfect world, as 250,000 dead in Syria and untold sectarian horrors in Iraq and Yemen testify to sobering effect. The conflict fuelled by the guns and bombs of Assad, Hezbollah and IS and the cash and rhetoric of the al-Sauds, the Ayatollahs and Russia has only been compounded by foolish and wilful Western ignorance towards realities on the ground in Syria. Kerry will be hoping that in Vienna the world can begin to make amends.