Despite a decade of warming relations with Syria, President Recep Tayyip Erdogan was making a bid to become the region’s dominant power. The situation in Syria has since changed dramatically—but the Erdogan strategy has not, Stuart Rollo wrote in Wall Street Journal.

When the Syrian civil war broke out in 2011, Turkey was one of the earliest countries to invest heavily in the overthrow of the Assad government. Despite a decade of warming relations with Syria, PresidentRecep Tayyip Erdogan was making a bid to become the region’s dominant power. The situation in Syria has since changed dramatically—but the Erdogan strategy has not, Stuart Rollo wrote in Wall Street Journal.

The result is that Turkey has become a barrier to resolving the conflict. It wages war on the Syrian Kurds, ISIS’s most effective opponents. And the country now plays host to an elaborate network of terrorist, including ISIS.

Early on, Turkey wanted to foster a Sunni majority government in Syria, preferably run by the local branch of the Muslim Brotherhood. The plan was simple and elegant. But the Bashar Assad government proved more powerful than expected.

So-called moderate Syrian rebels have either been sidelined by terrorist group, or revealed to have been radical militants themselves.

Thanks to Islamic State, the war has spread to engulf Iraq. And yet, as a global consensus solidified about the importance of defeating ISIS, Turkey has continued to play the game as if it were 2011.

This summer, for example, the Erdogan government came to an important agreement to let the U.S. use two of its air bases for strikes against ISIS. Yet Turkey has used the same bases to attack Kurdish forces in Iraq and Syria. The Erdogan government remains more concerned with limiting the power of the Kurds in Syria than with defeating ISIS.

Incirlik Air Base

Turkey has gone from being viewed by Western government officials, media and academics as an influential, moderating force for regional stability and economic growth, to a tacit supporter, if not outright sponsor, of international terrorism. It is also viewed as a dangerous ally that risks plunging NATO into an unwanted conflict with Russia.

When Russian President Vladimir Putin labeled the Erdogan government “accomplices of terrorists” after its fighter planes downed a Russian jet on Nov. 24, he was bluntly rewording an accusation that has been made repeatedly, but more diplomatically, in the West. The accusation: Turkey allows oil and artifacts looted by ISIS to flow across its border in one direction, while foreign terrorists, cash and arms travel in the other.

Speaking last year of the porous Turkey-Syria border, US Vice President Joe Biden let slip, in a moment of candor, that the biggest problem the U.S. faced in confronting ISIS was its own allies. More recently, on Nov. 27, a senior Obama administration official described the situation to this newspaper as “an international threat, and it’s all coming out of Syria and it’s coming through Turkish territory.”

Turkey has figured that its important position in NATO as a bulwark against Russian power would shield it from criticism by its Western allies, and buy it enough time to shape the Syrian conflict in its favor. But Russia has effectively turned the international sympathy over the downing of one of its jets into increased sway in Syria.

Mr. Putin has promised to “immediately destroy” anything that threatens Russian forces in the country. He also upgraded the local Russian arsenal to show that he can make good on his promise.

Mr. Erdogan’s best chance of achieving his goals is as a committed member of the U.S.-led coalition. He can then help the coalition remain in a strong position to negotiate, with Russia and Iran, a settlement of the Syrian conflict and the future of Mr. Assad, Wall Street Journal reported.

Kurdish Fighters

Turkey also needs to accept the move toward Kurdish autonomy in Syria as a fait accompli. The Kurdish Democratic Union Party, which Turkey officially categorizes as a terrorist organization, now fights ISIS alongside the U.S. and receives arms and training from a swath of Western countries.

Through its bravery and effectiveness, this group now has substantial international political capital.

Kurdish autonomy in Syria does not necessarily mean increased separatist activity in Turkey, any more than the creation of the Kurdish Regional Government in Iraq did. But Mr. Erdogan does need to negotiate peace with the Syrian Kurds, with clear terms for territorial integrity and respect for Kurdish rights. Turkey did so with the Kurds in northern Iraq, and now enjoys robust relations with them.

Failure to redirect its policy in Syria can only lead to Turkey’s further isolation and reputation as a reactionary pariah—and the continuation of a horrendous conflict. This is not the ascendant trajectory that the country has sought over recent decades.