The sudden decision by President Trump to endorse Turkey’s move to send its troops into Syria and pull out most of the American forces posted there seems to have shocked the country’s political and military establishment. American analysts and policymakers see events of the past week as largely benefiting Russia, the Syrian government, the remnants of the Islamic State and Iran.

Amid the great clamor of commentary, the United States and Europe are erroneously banking on sanctions on Turkey to contain the fallout. The harsh truth is that the United States, Europe and Turkey share responsibility for the creation of this crisis. They have all made a series of policy mistakes since the beginning of the Syrian war in 2011.

Sinan Ülgen
Sinan Ülgen is a senior fellow at Carnegie Europe in Brussels, where his research focuses on Turkish foreign policy, nuclear policy, cyberpolicy, and transatlantic relations.
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For the United States, the main failure was to naïvely believe that the partnership established with the People’s Protection Units, or the Y.P.G. — an organic offshoot of the Kurdistan Workers’ Party, or the P.K.K., which is considered by Ankara, Washington and Brussels to be a terrorist group — could be long-lived. Oblivious to the huge and negative impact of this commitment on bilateral ties with Turkey, the White House followed the Pentagon’s recommendation based on its an assessment that the Turkish counteroffer, of a group of Syrian opposition fighters trained by both Turkey and the C.I.A., would be inadequate to carry the fight against the Islamic State.

Nevertheless, Turks never came to terms with the United States siding so clearly with a group they consider to be a core national security threat. And American support for the Y.P.G. pushed it toward a perilous overreach. Kurds constitute about 10 percent of Syria’s population but with American support, they came to control almost one-third of its territory.

Turkey’s big mistake was betting on radical and Islamist elements of the opposition, such as the Syrian Islamic Liberation Front and the Tawhid Brigade, to achieve its goal of ousting Syria’s president, Bashir al-Assad. Ankara was less zealous, at least initially, than its partners in the West to join the coalition against the Islamic State, because jihadists were also fighting against Mr. al-Assad, along with other Syrian opposition groups.

Europe’s biggest failure was outsourcing its Syrian refugee policy to Turkey. Despite auspicious beginnings in March 2016, the refugee deal between Turkey and the European Union came under severe strain following a downturn in the Turkish economy. Turkey has been hosting about 3.6 million Syrians, with only about 100,000 living in camps close to the Syria border. The majority are in Turkish towns and cities.

As the unemployment rate rose to 13 percent, Turks in disadvantaged areas increasingly came to see the refugees as competing for their jobs and government resources. The rising anti-refugee sentiment played out in the municipal elections earlier in the year and contributed to President Recep Tayyip Erdogan’s Justice and Development Party losing control of Istanbul and Ankara.

Europe’s continuing resistance to a substantive resettlement program for Syrian migrants has created the political conditions for Mr. Erdogan’s government to seek another solution to this urgent problem. Ankara is justifying its cross-border operation into northern Syria as partly motivated by its desire to set up a safe zone, where at least a million Syrian refugees can be resettled.

Against such a political backdrop, American and European sanctions on Turkey will only backfire. They will be perceived as a reactive measure by Europe and the United States to penalize Turkey for unsettling the American plan to retain influence in the Middle East through its partnership with the Y.P.G. Sanctions could also decouple Turkey from the Western geostrategic orbit by weakening its allegiance to NATO — and accelerate its drift toward Russia and away from democratic values.

Turkey and the West need each other to influence the future of Syria. The United States and Europe need to shun the idea of sanctions and follow a results-oriented policy with Ankara. Sanctions will cost the United States and Europe the ability to work with the only NATO nation bordering Syria. It will have ill-fated consequences for a lasting and sustainable settlement of the refugee problem and a more effective counterterrorism policy to address the challenge of the remaining foreign fighters in Syria.

And Turkey will lose the ability to leverage the support of its Western partners for its regional objectives. Turkey will be politically and diplomatically isolated in the negotiations for a political settlement in Syria, where Russia and Iran will play a major role.

Russia has already emerged as the most powerful piece on the Syrian chessboard. Moscow rapidly facilitated a deal between Mr. al-Assad’s regime and the Y.P.G., which allowed the Syrian Army — for the first time since 2012 — to take control of significant towns such as Manbij in northern Syria, which had been controlled by the Y.P.G.

The outcome is perfectly in line with Russia’s envisaged endgame — to ensure that Mr. al-Assad extends territorial control to all of Syria. And in the meantime, Moscow intends to force Turkey to reconcile with Mr. al-Assad.

Instead of sanctions, the United States and Europe need to devise a mutually agreed plan of action with Ankara that would incorporate three major elements. First, they need to acknowledge that the policy of support to the Y.P.G. has ended; no long-term constructive engagement with Turkey can work otherwise.

Second, Turkey, the United States and Europe should restart a strategic dialogue to foster a common approach to the constitutional order and security arrangements for a new Syria. Otherwise, Moscow and Tehran will be in increasingly strong positions to reshape the regional order.

And third, Turkey’s Western partners should encourage Ankara to return to an agenda of domestic political reforms, which would also tackle the country’s longstanding conflict with the Kurds.

An end to the Western policy of arming the Y.P.G. and ensuring that northeastern Syria will not be used as a zone to challenge Turkish national security will create the right conditions for Turkey to overhaul its ailing political system and expand the sphere of liberties.

This article was originally published by the New York Times.