The Syrian war is one of the worst political and humanitarian crises since the Second World War and mediation attempts have proven largely fruitless. What are the reasons behind their failure, and what are the prospects for peace in the future?

January 2017 will see new leadership both at the UN and in the US. António Guterres will become the 9th Secretary-General of the United Nations and Donald Trump will take office as the 45th President. These leaders will inherit from their predecessors a problem that ranks among the toughest and most complex in the world today: the Syrian civil war a, conflict that began in 2011 and since then has seen between 312,000 and 470,000 deaths.

Both men have declared Syria a policy priority. Trump has given few specifics beyond a desire to depart from current U.S. policy, whereas Guterres has said that, under his leadership, ending the Syrian civil war will be the UN’s most important task.

Guterres faces tough odds: the catalogue of failed mediation efforts in Syria has by now grown quite long. After the Arab League’s failed attempt in the early phase of the conflict, the UN dispatched to Syria first Kofi Annan and then Lakhdar Brahimi, both of whom fervently tried to broker various ceasefire arrangements, and both of whom returned empty-handed. More recently, the diplomatic initiative has rested with U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov, who have sought to find a way to collaborate on Syria despite diverging priorities.

In September 2016, this duo managed to negotiate a ceasefire, but, in a rather typical display of how tenuous progress is in Syria, the deal fell apart within days, following an ill-timed accidental American bombardment of Syrian troops in Deir el-Zour and unrelenting combat in Aleppo. In parallel, Staffan de Mistura, the UN’s third envoy since the war began, has continued to probe for breakthroughs, however small and local, to keep a semblance of a process alive, but without substantive progress.

Why Syria is a mediator’s “mission impossible”

There are several reasons why previous mediation has fallen short in Syria. International disunity and distrust in the various mediators are important factors – rebels rejected the most recent UN initiative, a limited humanitarian ceasefire in Aleppo, on the grounds that the UN was “biased” against them. The main explanation, however, lies in the nature of the conflict. Kofi Annan labeled it a mediator’s “mission impossible”: a war fought between many and fractured coalitions, infused with sectarian enmity, and subject to constant meddling from foreign powers.

Academic research sheds light on all of these factors, and why and how they effect peace mediation. First, the higher the number of belligerents, the harder a conflict is to settle. In Syria, where the number of actors is extraordinarily high, it has proven impossible to design a deal that is attractive to a critical mass of parties. This problem has been particularly acute with respect to the opposition, which frequently have fallen to infighting and agree on little beyond the necessity of ousting President Bashar al-Assad.

Second, historical evidence shows that conflicts where belligerents anchor their demands in religious traditions are more intractable than other conflicts. In Syria, religious fault lines have gradually hardened, especially between Sunni and Shia, raising the threshold for peace deals that depend on sectarian co-existence. The widespread presence of jihadists who view the conflict in cosmic, Manichean terms add one further barrier to initiating a process premised on the exchange of concessions.

Third, with the possible exception of the Islamic State, nearly all actors in Syria enjoy the material and diplomatic support of foreign sponsors. Conflicts that attract external interventions tend to be more resistant to mediation, most likely because foreign powers can offset shifts on the battlefield by escalating the influx of weapons and other resources to their preferred client. Further, support from foreign sponsors makes belligerents less dependent on support from the local population, which otherwise can generate social pressure that incents negotiations.

Combined, these factors have created a situation where it has been difficult for mediators to identify a viable power-sharing deal, and even less, generate firm expectations that such a deal could be implemented.

The conflict will end, but how?

Like all wars, the war in Syria will end. The question is how long it will take and the means through which this will be achieved. Logically, the war in Syria can end in three ways: through a military victory, by petering out into a “cold war”, or via a negotiated agreement.

Even though the majority of civil wars end in military victory, most analysts have held the view that this is an unlikely outcome in Syria. Neither side has had the resources to impose, much less maintain, a monopoly on violence in the entirety of the country. However, there are signs that a regime victory has become, if not likely, at least a possibility. The fall of Aleppo to regime troops in December 2016 will free up considerable forces that can be reallocated for tactical offensives in other areas. Continued Russian efforts and a realignment of U.S. priorities in Syria under a Trump Presidency may allow the regime to make further gains.

Another scenario is that the war gradually de-escalates into a “cold war”, with little or no active fighting. In parts of the country, especially the South, this is already the de facto situation, as localized truces and standoffs have produced a state of suspended warfare. A generalization of this scenario, though, is premised on the exhaustion not only of the primary belligerents (e.g., via manpower shortages), but also of their foreign sponsors, which would require significant shifts in both regional and international politics.

The third way the war can end is via a negotiated agreement, either induced via external mediation of the kind discussed above, or emerging from direct negotiations between the parties within Syria. We know from statistical research that a growing number of civil wars end in negotiated agreements, but, in light of the challenges listed above, there is clearly some way to go before that will happen in Syria.

A changing landscape?

As neither of three paths to peace appears imminent, continued war is therefore the only realistic scenario in the short- to mid-term. But there are signs of a changing landscape, both militarily and politically, which may open up avenues to a negotiated agreement, at least in limited forms between the regime and the non-jihadist opposition.

The most important shift, potentially, is the election of Donald Trump as the next U.S. President. While the details of the President-elect’s Syria policy remains opaque, it is likely to include two ingredients: more direct coordination with Russia and stronger military efforts against the Islamic State. With Trump as President, the U.S. may be willing to shift publicly on issues that are currently recognized only implicitly, such as the acceptance of Assad’s staying in power, the failure of train-and-supply efforts, and the Islamist domination within the opposition. The current battery of economic sanctions may also be revisited.

The coming of Trump is therefore likely to favor Damascus, but it could also increase the prospects for substantive negotiations. Historically, when great powers favoring opposing belligerents in a civil war come together, it have tended to favor negotiated outcomes. If Russia, Turkey and the U.S. can maximize their leverage with their respective clients, they could help push them to the negotiation table. But chances are still slim: they have tried before without succeeding and Trump’s Syria policy may alienate the opposition, reducing U.S. leverage.

The fall of Aleppo signifies another important change in the strategic landscape. By capturing the city, regime forces dealt a demoralizing blow to the opposition, while further alienating Western audiences. It remains unlikely that the regime can claw back all lost territory, let alone rule it in a legitimate manner, but the victory in Aleppo may add further leverage to its strategy of seeking local “reconciliation agreements”. Several hundred such local truces have already been struck across the country and, if generalized, may portend a demographic “sorting out” that would leave Syria organized into more or less autonomous zones, akin to the  “cold war” scenario above.

For its part, the UN is likely to continue its valiant search for solutions, small and large. If the new UN Secretary General is to deliver on his promise to prioritize a peaceful solution in Syria, he needs to find a way to capitalize on the expected rapprochement between Russia and the U.S. His man in the field, envoy de Mistura has signaled that he concurs with the military fight against the Islamic State but that a military strategy needs to be accompanied by “political devolution” in Syria. This indicates that the UN is considering an arrangement styled on Bosnia or Iraq – essentially power-sharing along sectarian lines – for Syria. Even if the UN manages to leverage the U.S. and Russia behind such a plan, however, it currently appears unlikely that the opposition would give up on its demands for regime change, and that Damascus, smelling military victory, would seriously consider it.

Magnus Lundgren is a postdoctoral research fellow at Stockholm University, Sweden. His research focuses on conflict resolution in civil wars and on decision-making in international organizations such as the UN. His most recent publications include ”Which international organizations can settle civil wars” and ”Mediation in Syria: Initiatives, strategies, and obstacles, 2011-2016”. He is the co-founder of the Multilateral Negotiation Project, a non-profit that seeks to enable better global negotiation processes. He can be followed on Twitter @magnusllundgre