MADRID – As 2016 comes to an end, the outlook for 2017 is shrouded in uncertainty. Tensions in the Middle East are rising, and populist movements have appeared in Europe and the United States.

In the Middle East, the tragic conflict in Syria continues, despite several fruitless attempts at rapprochement, which were marred by the fundamental disagreement about Syrian President Bashar al-Assad’s future role in any peace process or political transition. Meanwhile, over the past week, Syrian government troops, backed by Russia and Iran, have retaken almost all of Aleppo – once Syria’s largest city, now utterly devastated by the war.

The world’s priority for the coming year must be to achieve peace in Syria, which will require close regional and international cooperation. On December 27, Iran, Russia, and Turkey will hold a tripartite meeting in Moscow to discuss a political solution for the Syria conflict. That meeting, if it takes place, is likely to be overshadowed by the fallout from the assassination of Russia’s ambassador to Turkey. But it is nothing if not surprising that these parties, and not the US and the European Union, would be negotiating such an agreement.

One positive development this year came in March, when the EU and Turkey signed an agreement to address the refugee crisis. Turkey has now taken in some three million Syrian refugees since the beginning of the conflict. Although EU-Turkey relations are currently not at their best, the dialogue between the two sides must continue in 2017, not least because of their common interests, which are based not only on economic interdependence, but also on the refugee crisis and the collective fight against terrorism.

European politics next year, meanwhile, will be consumed by the Brexit negotiations. In March, the United Kingdom will likely invoke Article 50 of the Treaty of Lisbon, triggering the formal procedure for withdrawal from the EU. The challenge will be to reach an agreement that guarantees the wellbeing of future EU-UK relations. This will not be easy, and EU negotiators have already set a timeline of only 18 months. While much remains uncertain, what is clear is that if the UK wants to retain access to the European single market, it will have to accept the EU’s four freedoms, including the free movement of workers.

In 2017, several European countries will hold general elections, and there is a risk that isolationist, anti-European populist movements will make a strong showing. For the EU to lose a country as militarily and economically important as the UK is bad enough; but to lose a founding EU member state, such as France, would be tragic.

Fortunately, many Europeans’ views toward the EU actually improved in the aftermath of the Brexit referendum. But this will not lessen the challenge for EU governments in the year ahead. They must unite societies divided by powerful global forces, such as globalization and rapid technological innovation.

The Brexit referendum, followed by Donald Trump’s victory in the US presidential election, signaled the rise of populism in the West. But now that Trump is filling his cabinet with oligarchs and former military men, we have reason to doubt that he will keep his promise to govern without the Washington "establishment.”

Trump’s incoming administration is full of unknowns, but there can be no doubt that his rejection of multilateral institutions will endanger international efforts to cooperate on solutions to the world’s biggest problems. This holds peril for US-EU relations. In previous years, the Paris climate agreement and the nuclear agreement with Iran were rays of light in a world closing itself off to multilateralism. In the coming years, such rays may become scarcer still.

Now more than ever, we need the kind of dialogue that builds strategic trust between great powers. And yet, Trump’s statements casting doubt on continued US adherence to a "One China” policy vis-à-vis Taiwan could severely damage relations between the world’s two largest economies. Similarly, notwithstanding the pro-Russian leanings of some among Trump’s team, the US-Russian relationship also lacks strategic trust, owing to Russia’s military intervention in Syria, its invasion of eastern Ukraine, and its alleged interference in the US election.

The coming year will be particularly important for Europe. Relations between the EU and the US must remain strong, rooted in mutual respect for democracy, freedom, and human rights. After a turbulent 2016, and with little positive news in international politics, 2017 is shaping up to be a year of challenges and uncertainty. But the biggest uncertainty of all is whether this is simply the end of another year, or the end of a geopolitical epoch.

The writer was EU High Representative for Foreign and Security Policy, Secretary-General of NATO, and Foreign Minister of Spain.Copyright: Project-syndicate