Turkey and Syria seem headed into a war. In the Syrian city of Idlib, at least 33 Turkish soldiers have been killed by Syrian shelling — with assistance from Russia — and 18 Syrians were then killed in retaliatory strikes. Conditions for the nearly three million refugees are horrific, with children dying and large groups on the move by foot, trying to break out of this Levant killing field.

The Syrian civil war should by now be over. Perhaps 11 million Syrians have been displaced, and more than 500,000 killed. Assad, using a horrific mixture of military tactics — nerve gas, barrel bombs dropped from helicopters, attacks against hospitals and schools, and torture of prisoners — has managed to crush the rebellion down to this final corner of the largely destroyed country. He has been abetted every step of the way by Russian President Vladimir Putin.

But now there is a fly in the ointment: President Recep Tayyip Erdogan of Turkey.

When I was the supreme allied commander of NATO at the early stages of the civil war, the long, vulnerable Turkish-Syrian border was a deep concern. I was asked repeatedly at briefings with allied heads of state why Russia was so deeply supportive of the Syrian regime.

I explained that there was more to it than Putin’s desire to show the world his loyalty to a long-term ally. He felt that engaging militarily would diminish U.S. influence in the region, ensure Russia’s access to warm-weather ports on the Mediterranean and enhance his sway with Iran (which also supports Assad). He also wanted to demonstrate to the Russian people that he was a decisive global player unafraid to stand up to the West.

His strategy remains coherent, and it appears he will succeed in helping Assad crush the rebellion.

Turkey has been opposed to Assad and aligned with some of the rebel forces for years; hence its deploying troops to Idlib.

Like Putin, Erdogan is pursuing a larger strategy in the region. He wants to control the Syrian border to diminish attacks in Turkey by Kurdish terrorists from the south, and to exert Turkish influence across the former Ottoman Empire.

He also aims to demonstrate to his political base in Turkey that, like Putin, he is an authoritarian man of action. He figures the ends are worth placing at risk the strong economic ties between the two nations, tourism from Russia, and a cordial personal relationship with Putin.

Erdogan has hardly been an ideal ally recently: sending his troops to slaughter U.S.-allied rebels in Syria, purchasing an advanced missile-defense system from Russia, and threatening to shut down NATO installations on Turkish soil, among other provocations. Still, the potential of a military collision between Russia and Turkey is of far greater concern for the NATO alliance. If the two nations’ troops end up in direct combat, Erdogan could call on the rest of NATO for assistance against a military great power.

We’ve been here before. During my time at NATO, we saw several incidents involving Russian and Turkish fighters and defense systems. Eventually we ended up deploying Patriot air-defense batteries to southern Turkey. That forced Assad and his Russian allies to concentrate on other parts of Syria to avoid an accidental clash with NATO.

This time, with significant land forces in close proximity and active combat underway, the chances of a miscalculation are far higher. Last Wednesday, Erdogan insisted that Turkey would not take even the “smallest step back” in an escalating standoff with Russia. He also called for again sending Patriot batteries to his southern border.

From an alliance perspective, there are a handful of actions that might ease tensions and avoid an open conflict triggering Article 5, the guarantee that an attack on one member of NATO is an attack on all. The top NATO brass and Secretary General Jens Stoltenberg need to meet with their Turkish counterparts and make the case for doing everything to avoid Russian forces on the battlefield — which of course is easier said than done.

NATO can provide what militaries call “deconfliction” between Russian and Turkish forces by providing high-level intelligence about Russian troop deployments and intentions. It can also technically assist Turkey with developing preventative protocols to avoid combat with Russia. The U.S. and Russia do this, for example, at sea, where we have very specific rules about approaching each other’s ships and aircraft, the so-called Incidents at Sea agreements. NATO can also provide logistical and humanitarian assistance to the refugee population.

Most important perhaps, the U.S. must let Moscow know in no uncertain terms that the consequences of combat operations against Turkish troops would include further sanctions and greater military support for Turkey in accordance with the NATO treaty — to include, for example, the Patriot deployment Erdogan has requested.

Clearly, there needs to be a global response to the violence in Idlib, and the United Nations Security Council must address this with more than calls to action. The idea of a negotiated “safe zone” between Turkey and Syria is still worth pursuing, although Assad and Putin feel they have all the momentum at the moment.

It’s unlikely we can avert the tragedy facing three million Syrians civilians — many women and children — about to be crushed between Putin’s and Erdogan’s competing strategic plans. Still, things would get immeasurably worse for everyone in the case of a full-blown NATO-Russia confrontation. Without nuanced U.S. and NATO efforts to both rein in and protect the interests of their fractious Turkish ally, that isn’t an unthinkable result.

James Stavridis is a Bloomberg Opinion columnist. He is a retired U.S. Navy admiral and former supreme allied commander of NATO, and dean emeritus of the Fletcher School of Law and Diplomacy at Tufts University.

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