Who gains in the battle for Syria's northeast?

President Donald Trump's decision to pull out of Syria radically realigns the balance of power in the country's northeast and creates a vacuum which Russia, Turkey and Iran are racing to fill.

Turkish President Tayyip Erdogan says he wants to settle up to two million Syrian refugees, many of them of them Sunni Arabs, into the region targeted in the operation, territory which is currently controlled by Kurdish-led forces. Despite global criticism, Erdogan has said nothing will stop operations against Kurdish YPG fighters, considered terrorists by Ankara because of their links to guerrillas waging an insurgency in southeast Turkey.

The full withdrawal of United States forces and deployment of the Syrian army is a major juncture in the Syrian conflict, restoring a foothold for Assad's government across the biggest swath of the country that had been outside its grasp. The area includes oil, farmland, water resources and the hydro-electric dam at Tabqa, vital assets that will better position the government to cope with the impact of Western sanctions. Assad's army, however, has been weakened by the attrition of prolonged conflict, and now relies heavily on Russia, Iran and Iran's Shi'ite militia allies including Lebanon's Hezbollah.

Syria's Kurdish groups exploited the withdrawal of government forces from the northeast at the start of the Syrian conflict to build up the institutions of autonomy and teach Kurdish language in local schools. Exposed to Turkish attack by the United States withdrawal, they invited the Syrian army back, a decision that highlighted their weakness and signalled an end to many of their dreams. They will hope to preserve as much of their autonomy as possible in political talks with the Syrian state, their long declared objective. But they no longer have a powerful ally to back them.

The SDF says the Turkish offensive has helped energise Islamic State sleeper cells, just a year after the "caliphate" was effectively dismantled. Islamic State has already claimed responsibility for attacks, including a deadly car bomb strike outside a restaurant in the biggest Kurdish city Qamishli just a day after Turkey launched its incursion. Since the fighting started last week, the SDF says there has also been unrest in the prisons where they are holding the fighters, and in camps holding their wives and children.

Assad’s ally Iran is also set to gain. Iraqi paramilitary groups backed by Iran on the Iraq-Syria border will likely help Assad secure control, strengthening their own supply lines along a corridor of territory from Tehran to Beirut.

Russia's indispensable role in Syria reflects a larger shift in the Middle East from Damascus to Riyadh, as showcased by President Vladimir Putin's Gulf tour this week, including his first visit to Saudi Arabia in more than a decade. It was Russia's intervention with air power in 2015 which helped turn the tide of Syria's civil war in Assad's favour, and Trump's decision to pull out of the northeast has cemented Moscow's central role in shaping the country's future. The two countries may be able to forge an agreement dividing the northern border into new control zones and prevent their local allies, the Syrian government on the one hand and anti-Assad insurgents on the other, from going to war.