Turkey upped the stakes of the already ruinous Syrian conflict after it launched a direct offensive across its southern border, targeted ostensibly at Islamic State positions in the northern Syrian town of Jarabulus. With the support of U.S. forces, Turkish tanks motored into Syrian territory in the early hours of Wednesday. By the afternoon, the state-run Anadolu Agency published images of Turkish-backed rebels entering Jarabulus on the back of pickup trucks.

Ankara labeled the operation Euphrates Shield, a reference to the river that threads through Turkey, Syria and Iraq. It was carried out just days after an alleged Islamic State suicide bomber hit a wedding in the southern Turkish city of Gaziantep. Authorities there declared a section of Turkish territory along the border to be a "special security zone," and a government communique warned journalists from attempting to report in the area while Turkish forces and allies "cleared" the Jarabulus district of Islamic State militants.

Yet Turkish officials also made clear that the operation wasn't simply about targeting the militant group. Ankara has long worried about the advances of Syrian Kurdish militias in northern Syria. The most prominent faction are the People's Protection Units, or the YPG — key fighters in the ground war against the Islamic State and recipients of American aid, but a group that Turkey sees indelibly linked to outlawed Kurdish insurgents operating within its borders.

When a coalition of rebel units known as the Syrian Democratic Forces, which includes the YPG, captured the northern Syrian town of Manbij this month from the Islamic State, the victory led to scenes of joy among its residents, who had suffered under months of extremist rule. But Turkey wasn't so thrilled. It considers the YPG crossing over onto the western bank of the Euphrates, where Manbij sits, a "red line."

The Islamic State, also known as ISIS and ISIL, has held Jarabulus for a number of years, so the timing of the Turkish incursion is curious.

On Monday, Turkish forces shelled YPG positions in Manbij. And as the advance toward Jarabalus pressed ahead, Turkey's foreign minister issued a warning on Twitter to Syrian Kurds there.

Ibrahim Kalin, a senior spokesman for Turkish President Recep Tayyip Erdogan, signaled Turkey's long-standing argument that the fight against the Islamic State is the same as Ankara's struggle with Kurdish terrorism.

"The purpose of the Jarabulus operation is to clean up all the terrorist elements including ISIS and YPG," Kalin tweeted. "Turkey's determination is whole."

Moreover, Vice President Biden, who was in Ankara on Wednesday as the senior-most U.S. official to visit after a failed coup against Erdogan last month, articulated Washington's support for Turkey's position, saying the YPG and its allies risked losing U.S. backing if they didn't heed Turkey's demands to retreat to the east bank of the Euphrates.

"We have made it absolutely clear to those elements that are part of the SDF, the YPG that participated, that they must move back across the river," Biden said, according to The Washington Post's Karen DeYoung. "They cannot, will not, and under no circumstances get American support if they do not keep that commitment. Period."

Aldar Xelil, a senior YPG commander, wrote on his Facebook page that the Turkish operation was "a violation of Syrian sovereignty" and "a declaration of war on all the sects of northern Syria."

What follows is a complex rejiggering of the geopolitical chess game in Syria:

  • Turkish officials see the need to safeguard a northern corridor from its borders to the beleaguered Syrian city of Aleppo for the rebel groups that it backs. Some of these factions have been battling both the Islamic State and the YPG and its allies and were getting squeezed in Aleppo's north. Turkey may probably revive the idea of creating a "safe zone" for refugees and humanitarian aid in this area.
  • The Turkish intervention puts a serious dent in Syrian Kurdish ambitions to stitch together a semiautonomous region in northern Syria. The YPG controls contiguous "cantons" in Syria's northeast and had hoped to inch closer to another Syrian Kurdish enclave tucked away in the northwest of the country.
  • It raises questions about the ability of the SDF and the YPG to march on Raqqa, the Islamic State's de facto capital in Syria, if faced with emboldened Turkish-backed forces on their western flank. These rebel forces include some Sunni militias that are increasingly embracing a radical, sectarian line.
  • And it also suggests Turkey's somewhat softening approach toward the regime of Syrian President Bashar al-Assad, which it has vehemently opposed since the beginning of the Syrian conflict in 2011. Regime forces have been suffering defeats to YPG units in northeastern Hasakah province over the past week. Ankara said it had notified Damascus ahead of its offensive.

What happens next in Manbij is as important as what happens after the Turkish-led recapture of Jarabulus. As Syria analyst Hassan Hassan wrote earlier this week, the largely Arab city is a vital testing ground for future reconciliation and unity in war-ravaged Syria.

"Manbij was a key stronghold for ISIS, and a city that can serve as a refuge for the hundreds of thousands of civilians fleeing regime violence in Aleppo and ISIS oppression in eastern Syria," Hassan wrote. "If Manbij is turned into a bastion of good governance, it will be no small success story. Due to its significance, the city’s stability and success will resonate far and wide."

For the time being, though, it remains yet another hot spot.

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