Syrian rebels, with the help of the Turkish military, are slowly making their way across northern Aleppo province. Turkey's primary objective in launching its offensive into Syria, known as Operation Euphrates Shield, was to block the path of Kurdish forces trying to form a link between their holdings in Afrin and Kobani cantons. And by all appearances, Turkey is on the verge of succeeding. Over the past few days, Ankara's rebel allies have capitalized on their decisive victory against the Islamic State in Dabiq by driving even farther south. As they have, the chances that the Kurdish People's Protection Units (YPG) could join the two cantons together have grown slimmer.
Galvanized by their diminishing prospects, the YPG and its allies struck out to the east, crashing headlong into the advancing rebel forces on Oct. 19. Turkey immediately targeted the Kurdish fighters with heavy shelling and airstrikes, which Ankara claims killed as many as 200 fighters. Skirmishes between the Turkish-backed rebels and the YPG have continued ever since, underscoring the deeply rooted animosity that exists between them in spite of their shared campaign against the Islamic State. With the fate of al-Bab — both a crucial crossroads in the Syrian conflict and the last link between the Afrin and Kobani cantons — at stake, the two could find themselves battling each other more than their common enemy in the weeks ahead.
But the Turkish-backed rebels have not forgotten their original purpose: countering Syrian President Bashar al Assad's government. As of now, the best way for them to do that is to march south to link up with their comrades around northern Aleppo. In fact, the rebel groups participating in Operation Euphrates Shield have made it clear that they intend to resume their fight against loyalist troops once they have dealt with the Islamic State and the YPG. The rebels are ousting the Islamic State from several key towns and villages as they go, depriving the extremist group of its access to a highly coveted source of recruits and taxes. In fact, this explains why the United States continues to be so heavily involved with the rebels alongside Turkey, embedding special operations forces within their ranks and providing them with air support.
Northern Aleppo is quickly becoming one of the most crucial theaters of the Syrian civil war. The rebel advance is not only hurting the Islamic State and hamstringing the Kurds, but it is also impeding U.S. efforts to seize Raqqa and loyalists' attempts to retake Aleppo city. Perhaps most important, though, Operation Euphrates Shield carries the risk of starting a brawl with Turkey and the United States on one side and Russia and Iran on the other — a fight whose consequences would reach well beyond Syria's borders.