FOR a moment it looked as though Syria’s seven-year war, which has killed more than 400,000 people and contributed to the largest refugee crisis in recent history, might be winding down. As 2017 drew to a close, the so-called caliphate of Islamic State (IS) had disintegrated. The forces of the Syrian president, Bashar al-Assad, and the rebels fighting to dethrone him had largely stopped killing each other. Russia, which had intervened to save Mr Assad, said its mission was “basically accomplished” and had promised to bring its troops home. But since then the calm has shattered. The regime has turned its guns on the rebels. Turkey has sent troops over its border to battle Kurdish forces. Americans have killed Russians. And long-standing tensions between Iran and Israel have flared. Why is Syria’s war heating up again?

Part of the answer lies in the collapse of IS and the scramble for territory that ensued. In October Raqqa, the capital of the self-styled caliphate, fell to the Syrian Democratic Forces (SDF), a Kurdish-led militia that America has used to fight IS. Mr Assad’s regime, keen to concentrate on retaking the lands occupied by IS, duly agreed to a ceasefire with the rebels. By December it was in charge of lands to the west of the Euphrates river, and the SDF controlled the lands to the east. But at that point regime forces once more took up the attack against the rebels. In January they sliced off parts of Idlib, the only province under rebel control. In February they launched one of the war’s deadliest bombardments on the rebel-held enclave of Eastern Ghouta, a suburb of Damascus.

The collapse of IS has also widened fissures among the foreign powers jostling for a say in Syria’s future. In January America’s secretary of state, Rex Tillerson, said American troops would remain in Kurdish-held parts of Syria until IS no longer posed a threat, and a political solution to the war had been found. This infuriated Turkey, a NATO ally, which considers some of America’s Kurdish partners, the YPG, to be terrorists. Days after Mr Tillerson’s announcement, the Turkish army assaulted Afrin, a YPG-controlled pocket of territory in north-western Syria. There are no American forces in Afrin, but Turkey’s president, Recep Tayyip Erdogan, has threatened to march on Manbij, a town which does have them. This heightens the risk of direct clashes between two NATO powers and their proxies. America’s vow to stay in Syria has also angered Russia, which backed Turkey’s operation in Afrin. Seeking to test America’s commitment to its campaign, the Kremlin may have ordered Russian mercenaries to attack an American-supported base in the east—an attack that left scores of Russians dead.

Worse may be on the way. Iran’s influence in Syria seems to be increasing, as it seeks to cement its position in order to ensure the supply of weapons to its Lebanese proxy, Hizbullah. Iranian-backed militias are creeping closer to the Israeli-occupied Golan Heights. In February Israel shot down an Iranian drone that had entered its airspace, before bombing an Iranian-controlled base in Syria. After Syrian air defences downed one of the Israeli jets, Israel retaliated with strikes against Syrian anti-aircraft batteries. Israel’s fears grow in step with Iran’s influence. Although neither side appears to want a war, many reckon a larger conflict is inevitable. On February 24th the UN Security Council agreed to a 30-day ceasefire, but it looks set to fail; Turkey, Iran and the Assad regime have all said they will continue fighting. With tensions rising among foreign powers, Syria’s intractable war will become even more impervious to peace, and its civilians will continue to bear the brunt.