Garvan Walshe is a former National and International Security Policy Adviser to the Conservative Party. He runs TRD Policy.

When a civil war in a neighbouring country allows terrorists and guerrillas to flee next door, establish territorial control, use it as a base from which to train, supply and provide medical assistance to their forces, and even use it as a base from which to launch attacks, the temptation to use your regular army to crush them is hard to resist. Territory gained is territory from which attacks cannot be launched. More strategically it is a foothold form which to press your national interests in any negotiations that might bring the war to an end.

We don’t have to go back to Gustavus Adolphus’s invasion of Brandenburg in 1630 to understand how intractable such interventions, even when geographically contiguous, can get. When Israel invaded Lebanon in 1982, early military and even political success (the then president Amine Gemayel even signed an agreement to normalise relations with Israel in 1983), led to 20 years of guerrilla war, international opprobrium and the rise of Hezbollah.

Hezbollah, of course, would later be as instrumental in preventing Bashar Assad losing power in Syria as Assad’s father was in derailing Israeli plans in Lebanon. And it’s Syria where a neighbouring power is as much in danger of committing a terrible mistake as Israel was in the 1980s.

The neighbouring power is Turkey, and the operation is a buffer zone Ankara has been seeking to carve out on its southern border. From Turkey’s perspective, the case for intervention is strong. The Kurdish-dominated Syrian Democratic Forces, which control the area in question, are inextricably linked with the Kurdish terrorist organisation, the PKK, which has waged a bloody terrorist campaign for independence for decades (though secular, and traditionally Marxist, they practice suicide bombing).

The SDF however are also inextricably linked with the United States and the international coalition against Daesh (ISIL). The US and France have troops on the ground advising them, and planes in the air protecting them. Turkey has for some time sought to push Donald Trump to withdraw American troops, and almost managed to do so last December, leading to the resignation not only of Brett McGurk, the American official in charge of anti-ISIS operations, but even James Mattis, the US Defence Secretary.

Forty-eight hours ago, Erdogan tried again. Trump tweeted his announcement of a withdrawal (catching the SDF, France, and even Mattis’s replacement at the Pentagon by surprise), and Turkey announced it would start military operations.

This has further heightened America’s political crisis, with numerous Republicans, most of whom had been merely silent following Trump’s attempt to pressure Ukraine into inventing corruption allegations against one of his 2020 opponents, to condemn him. Lindsay Graham, the Republican chairman of the Senate Judiciary Committee, threatened sanctions and even Mitch McConnell, a study in circumspection when it comes to asserting legislative authority against the executive, thought to rebuke the President. Trump responded to the pressure with another bizarre threat to obliterate the Turkish economy (something he claims he’d already done before).

Meanwhile, Sergei Lavrov, the Russian Foreign Minister, preened his feline whiskers, called for calm and offered to mediate. The Security Council, which meets today, at Paris’s request can be expected to deadlock. The situation on the ground however, is becoming increasingly urgent.

Though there cannot be said to be anything as coherent as Western policy in Syria, the SDF are strategically aligned with Western interests there. Their impeccable propaganda: female soldiers driving Daesh from Raqqa’s Margaret Atwood-inspired dystopia; Western volunteers training side by side with local troops, and the adoption of a post-Marxist secular environmentalist creed to replace their traditional Leninist ideology, should not disguise their military effectiveness. They provided the ground troops that defeated ISIS, and currently guard some 15,000–20,000 prisoners, mainly from Western countries.

Now they insist that under pressure from the Turkish threat they have no manpower to spare for the task and are threatening the US with allowing a jailbreak. Trump, whose only understanding of negotiations is to screw his partner, hasn’t realised they can screw him back. The American Army is furious at being told to abandon their allies without whom the so-called Islamic State would still be in existence. They know, too, that “we’ve been told to abandon you, and can you please help us extricate our men from here” isn’t a winning offer.

The greatest strategic difficulty however is Turkish. Ankara officially has two aims for the campaign: first, to use Israeli terminology again, to eradicate the “terrorist infrastructure” that the SDF provide to the PKK. Second, to find somewhere to settle a portion of the millions of Syrian refugees currently in Turkey. They aim to do this by establishing a buffer zone, some 30 kilometres into Syria.

Entirely coincidentally, this zone contains every major Kurdish population centre. Behind them is only desert. Settling the refugees in these towns (which isn’t, incidentally, where they are from) will, it thinks, prompt a building boom, as it has in areas inside Turkey where a Kurdish insurgency was crushed in the past 18 months. Let’s just say this: the organised settling of a new population in an area occupied by hostile locals can on occasion be successful, but it is not something that has ever produced peace.

In tactical terms, Turkey asserts, as everyone does these days, that it only aims at the terrorists, and not the civilian population. It also asserts that its superior air force and artillery will make short work of any opposition. This is nonsense. In reality they are hoping that the SDF will flee, as they fled from Afrin, to the west, in an earlier round of confrontation. When they fled from Afrin, they could at least go to Kurdish-held North West Syria, but now Turkey proposes to take precisely that territory away from them.

That is the first mistake. If they’ve nowhere to go, they’ll have no alternative but to fight. There are two ways to defeat an enemy entrenched in urban centres: hard street-by-street fighting in which thousands of your own men will be killed; or what might be called the Russian school of counterinsurgency, as practiced on Aleppo, in which tens of thousands of their civilians are murdered.

Neither is an appetising choice. The fact that this decision has been taken and the arguments advanced for it suggest more that decision-making within the Turkish state has broken down; that since the coup, the military have been unable to block Erdogan’s ill-thought through impulses, and Turkey is about to commit a historic mistake whose consequences for Syria, the region and Turkey itself will be calamitous.