The dusty roads of Azaz, just off the Turkish-Syrian border, used to be the sort of place you whizzed through on the way to rebel-held Aleppo. Now it is the scene of seismic changes to the war in Syria, which could decide the most complex and unresolved question of the conflict: who will fight for Syria’s Sunni Arabs? Hospitals in Azaz were hit by a rocket strike Monday, but the area has also been the scene of fierce clashes. Contesting the town are two groups: Syrian Sunni rebels, many backed by Turkey, Gulf states and sometimes the U.S., are facing an advance from the Syrian Kurds known as the YPG, another group that receives U.S. support. Why this region matters: A rock and a hard place It will help if you look at a map: Essentially this fight is for the slim tranche of territory these relatively moderate Sunni rebels used to consider their stronghold and that used to be the vital supply route into Aleppo. In the past 10 days, all that has changed. The Assad regime has moved fiercely into the south of the area, cutting off the supply route to Aleppo. Then, in the past few days, the Syrian Kurds have moved east out of Afrin, the enclave north of Aleppo in which they had stayed peacefully for years, and taken territory quickly from moderate Syrian rebels. On Monday night a leader with the Syrian moderates told CNN that the Syrian Kurds had taken Tal Rifaat, a vital town to the south of Azaz. This means they only have to advance mere kilometers east before they reach the front lines with ISIS that the Syrian moderate rebels have fought to defend for months. As of Tuesday afternoon, reports were emerging the Syrian Kurds had struck a deal to enter the key town on that front line – Marea – without a fight. This leaves the U.S. as an awkward spectator to a fight between one group it has been supporting with limited success – the Syrian moderate (Sunni Arabs) rebels – and another group which has thrived with its assistance – the Syrian Kurds. The U.S. will do what it can to pressure the Kurds to turn back, but it may be too late. One of the Syrian moderate rebels told CNN he believed the Syrian Kurds were getting arms from the Russian and regime forces to their south. The rebel, who has strong ties to the U.S., told CNN: “We have strong evidence that (they) are coordinating with the Russians, who have been providing a lot of support. We have already submitted this evidence to the Americans.” He echoed what many observing the Kurdish advances have feared: that they are part of a land grab by the Kurds to bolster their ambitions for a state of their own. This idea terrifies NATO member Turkey, which sees the Kurds as the major threat to its state. The Kurdish move east brings them closer to their dream of uniting Afrin with the town of Kobani and creating a contiguous Kurdish state along Turkey’s long southern border. “We will take part in the battle against them because they are trying to change the demographic of the land,” the Syrian Sunni rebel told CNN. “It has been Arab land for thousands of years; they want to change it with Kurdish leadership. But they are dreaming. This will never happen.” Yet such sentiments may already be too late: The advances are swift and the Syrian Kurds have historically been successful at holding territory. For their part, the supporters of the Syrian Kurds claim they are cleansing the area of radicals among the rebel ranks. Things are moving very fast – and the changes may alter the course of U.S. policy in the war. On the front lines of the battle for Aleppo But why is this tiny patch of land, and the ramshackle moderate rebels who hold it, so important? It’s because they are – in the north of the country, at least – all that remains of the moderate Sunni Arab forces the U.S. has long courted to attack ISIS and, possibly later, confront the Syrian regime. Their defeat could put an end to the international coalition’s goal of finding a moderate Sunni force as a partner in the fight against ISIS and to represent the millions of Syrian Sunnis who began the rebellion against Assad. Granted, there are moderate forces in the south of Syria who have been getting Western aid, but they are mostly not fighting ISIS. And the pockets of moderates around the country that remain have been hit hard and are tricky for outside aid to reach. It has been in the north that the bulk of the US effort has focused. For this reason, the advances around Azaz have had greater impact. It’s been the failure of moderate Sunni Arabs in Syria to find a cohesive political and military voice that has been behind the rise of ISIS. This is how we got here: Failure of moderates Back in 2012, when the revolution became a civil war, most of the fighting against al-Assad was done by moderate Sunni Syrians: schoolteachers or plumbers who had taken up arms and sought a better life. They were bombed relentlessly by the regime, yet persevered. In many ways, they were this long war’s first and indisputable heroes: protecting themselves and infected by the dizzy and unattainable ambitions of the Arab Spring. But they lacked proper political leadership. The Syrian opposition leaders became a bit of a five-star farce, lounging around in luxury hotels. They bickered amongst themselves so fecklessly that it became hard to keep track who was actually their leader. These endless squabbles began to frustrate international supporters. Then 2013 came and the Assad regime was still holding on, even crossing President Barack Obama’s famous red line of chemical weapon use, all to no military consequence. Meanwhile, radicals began to seep into the rebel ranks. First it was the Nusra Front or al-Qaeda in Syria, considered by Hillary Clinton back then to be a simple extension of al-Qaeda in Iraq. Nusra were terrorists to U.S. eyes, but to many Sunni Syrians they were the ones doing the real fighting against the regime. There was little western support – but there was Nusra. The group continued to grow, joining a rebel coalition that saw tremendous success against the regime in late 2014 and 2015: the Army of Conquest. This alliance contained moderates, but also radicals, and al-Qaeda. It took huge swathes of territory from the Assad regime, prompting the Russian intervention. But it lacked western support as, beneath it all, al-Qaeda was doing a lot of the fighting. Simultaneously, in 2014, ISIS spread across the border from Iraq. Also Sunni, their initial benevolence toward the communities they swallowed was quickly usurped by a ghastly brutality that made them the international menace they now are. The U.S. found itself drawn into an air war against them, and found that the Kurdish forces to ISIS’s north-east were actually the most effective ground force they could use against them. Separately, the U.S. tried to train and equip moderate Sunni Syrians, and put aside half a billion dollars to do so. But the program’s lengthy screening process and ban on candidates fighting the regime sapped its appeal, until only 54 recruits emerged and the program ended. The moderate Sunni Syrian rebels continued to play their Gulf and western sponsors off against each other, and still resolutely failed to unite. Where are we now: Opportunity for radicals The Kurds are still America’s main ally in the fight against ISIS. But now they are advancing against the very forces the US have courted to fight the Assad regime: the moderate Sunni Syrian rebels. These moderates are now perhaps fatally weakened in a northern battlefield where the Kurds grow stronger daily; where the Assad regime continues to advance with Russian air support, trapping many anti-regime fighters inside the ruins of Aleppo’s east; and where even a beleaguered ISIS is using the chaos to retake some land. Now that Russia has joined the war, the geopolitical implications of this mess are staggering. Turkey still supports the moderate Syrian rebels, and has hinted that if Azaz falls to the Kurds it may intervene. But in doing so, it would intervene against America’s key ally in the war against ISIS: the Syrian Kurds. Turkey and the U.S. are NATO allies – and the prospect of their open disagreement must leave the Kremlin salivating. Syrian army: ‘Russian intervention a blessing’ This torturous scattergram of alliances leaves one group almost unrepresented on the battlefield, the greatest victims of the war – ordinary Syrian Sunnis. ISIS claim to represent them; al-Qaeda does a lot of the fighting to protect their traditional areas. But the moderate forces who began their rebellion in the north are in disarray. Now, as we have seen time and time again, radicals may well step into the void.