Donald Trump’s decision to deploy hundreds of US marines in northern Syria last week has received surprisingly little attention. The deployment pitches relatively inexperienced American soldiers into the middle of a highly toxic, multi-fronted battlefield that includes combat-tested Kurdish militias, Syrian army troops, anti-regime fighters and Russian, Iranian and Turkish forces.

The Trump administration says the aim is to defeat Islamic State (Isis) by assisting in the capture of the terrorists’ HQ in Raqqa. This forthcoming campaign is seen as complementary to the ongoing siege of Isis-held Mosul, in northern Iraq.

The defeat of Isis is plainly highly desirable and the international effort to do so is slowly coming to a head. Growing fears in Britain and Europe about the threat posed by returning Isis terrorist recruits are evidence of the belief in western capitals that this vile organisation and its fatuous caliphate will soon be dislodged from its principal strongholds.

But the simplistic idea, promulgated by Trump, that Isis and its warped jihadi ideology can be annihilated by force is foolish and naive. More dangerous still is Trump’s apparent belief that the US can focus solely on Isis while ignoring bigger questions about Syria’s future. In the space of a few chaotic weeks, Trump has overturned eight years of Barack Obama’s cautious policy towards Syria. Unlike Iraq, where Washington is co-operating with a mostly friendly government, the US faces the hostility of Bashar al-Assad’s regime, whose removal it still officially seeks.

The US marines and special operations forces, totalling nearly 1,000, are vulnerable to attack by larger groups more accustomed to the terrain. The dire consequences, should a US soldier be taken hostage by Isis, can only be imagined. At the same time, ostensible US allies, such as Turkey, cannot be relied upon, while Russia and Iran, Assad’s main backers, have no interest in ceding ground and influence.

The key, longer-term struggle is not over the fate of Isis, but the political control and territorial integrity of northern Syria and, by extension, Iraq. All the key players have differing interests. Assad wants his country back, whole and entire. Turkey wants a border “safe zone” under its control, principally to curb autonomy aspirations among US-allied Syrian Kurds. For their part, the Kurds want to be free of Damascus’s yoke and some would like to join forces with the self-governing Kurdish regional administration in northern Iraq, a prospect Ankara views as an existential threat, given its own large, disaffected Kurdish population.

Whatever Trump thinks about a new era in relations with Moscow, Russia, the real military power in the air and on the ground in Syria, will not help. It wants to minimise American leverage, in line with Vladimir Putin’s bid to project Moscow’s influence across the Middle East and Afghanistan.

This objective underlay last week’s summit between Putin and Recep Tayyip Erdoğan, Turkey’s president, at which the leaders buried old disagreements over Syria and pledged to work together to defeat terrorism. In Erdoğan’s view, this means the US-backed Syrian Kurds as much, if not more, than Isis. Erdoğan said Russia had agreed to lift all remaining sanctions imposed after Turkey shot down a Russian combat plane over the Syrian border in 2015. On the diplomatic front, meanwhile, Turkey is backing the Russia-Iran “peace plan” for Syria, which sidelines the US and Europe.

It is easy to forget that Turkey is a Nato member and EU applicant. Openly defying the west and reversing his previous stance, Erdoğan has now, in effect, joined Russia and Iran in supporting Assad. “We are working in full co-operation militarily in Syria. Our chiefs of staff, foreign ministers and intelligence agencies cooperate intensely,” Erdoğan declared in Moscow.

The unfortunate, but perhaps inevitable, corollary of this Russian-Turkish detente is Ankara’s repeated threat to further reduce security co-operation with the US unless it ditches the Syrian Kurds (which it has so far refused to do). Direct confrontations are thus possible between US and Turkish troops and their respective rival proxies, the Syrian Democratic Forces and the Syrian Free Army, whom US troops are tasked with keeping apart in the northern town of Manbij.

Trump’s Syrian intervention is “fraught with risk”, Robert Ford, former US ambassador to Damascus, told the Washington Post. “It is a huge policy change.” The potential for military escalation or “mission creep”, if and when US ground troops get into trouble, is obvious, vast and worrying. Northern Syria is a quagmire. Trump just jumped straight in.