The recent capture of the Syrian border town of Tal Abyad held by the fighters of the Islamic State of Iraq and the Levant (ISIL), by Syrian Kurdish forces (known as the YPG) is a major development in the course of the war in Syria.

The result is that Kurdish forces are now poised to control the vast majority of Syria's border with Turkey and now constitute a fighting force of some 50,000 fighters, backed by US airpower, operating in a united stretch of territory.

The Democratic Union Party (PYD) which largely represents the Syrian Kurds, has stated that its priority is now focused on uniting historical Kurdish areas of Syria (known as Rojava), stretching from Afrin to the Tigris river into one contiguous land mass. Additionally, it has signalled that defeating ISIL in its heartlands would not be anathema to solidifying its control across much of northern Syria.

This suggests that the YPG will push west towards the ISIL-controlled town of Jarabulus, moving weapons and manpower from the main canton of Jazeera to assist in any future offensive. The YPG is also expected to continue its push towards ISIL strongholds, by surrounding its de-facto capital Raqqa.

YPG strategic tactics

Wary of upsetting the local Arab population, YPG forces will most likely surround logistical supply routes into the city, cutting it off from the outside world, waiting for the right moment to strike deeper, in concert with local Arab partners and Free Syrian Army (FSA) and affiliated groups, backed by US airpower.

Much like their Iraqi brethren in Mosul, it is unlikely the YPG could take the city by itself, nor does it possess the will to do so. The group's openly Kurdish identity undermines its appeal in Arab areas, forcing the group to approach local Arab tribes for support. PYD messaging has been careful to stress that any future battle for Raqqa would be an operation in which Arab forces and the FSA would take the lead, supported by the YPG if required.

The group's openly Kurdish identity undermines its appeal in Arab areas, forcing the group to approach local Arab tribes for support.

The advance of the Syrian Kurdish forces in the areas surrounding Tal Abyad has been met with mixed reactions and is likely to be contested in any attempt to push south into ethnically Arab areas. Islamist rebel groups and sympathisers' brigades have condemned the group's offensive, and accuse the PYD/YPG of systematic ethnic cleansing.

The Kurds deny any such accusations, but admit that during the offensive allied fighters burned crops and destroyed the homes of suspected ISIL sympathisers. Kurdish Asayish (internal security) entered Tal Abyad shortly after its fall looking for ISIL collaborators, detaining a number of individuals, their status is as yet unconfirmed.

The US will need to consider these problems as the strategy develops. While the YPG may seem like good allies on paper, if Syria's central regions are alienated it is likely to cause only more trouble and internecine war. This may well pit the US-backed YPG against other rebel groupings that have the support of US allies, prolonging the conflict the US is trying to end.

US support

The US has supported the YPG for two reasons: Firstly, their offensive has been successful and is narrowly focused on fighting ISIL, rather than focusing first on regime forces. Secondly, in the PR war, public sympathy in the West has tended to view the Kurds as the most forward-thinking rebel group in the battle against extremism.

The same cannot be said for the myriad of factions receiving aid from regional backers - many of which have cooperated with al-Qaeda's Syrian affiliate, Nusra Front.

But the PYD's connections to the Kurdistan Workers' Party (PKK) - a US-, EU-, and Turkey-designated terror group - are problematic, and Ankara is deeply concerned with the group's advance and sympathetic treatment in the international media. But despite these concerns the US appears to be committed to maintaining its air support for the Syrian Kurds, both near the Euphrates in the west and the outskirts of Raqqa in the south.

The question for the US will be whether aiding an enemy of the Turkish state will impinge dramatically on their relationship with a NATO ally. To some extent the immediacy of "degrading and defeating" ISIL trumps concerns of longer term tension with Ankara.

The longer ISIL stays in place the weaker both Iraq and Syria become, and the more likely the chance of permanent state collapse. The US favours the maintenance of Syria's territorial integrity, but the counterpoint to this strategy is that by empowering Syrian and Iraqi Kurds, the result may be hastening the break-up of these countries anyway.

So by choosing sides, the US may be signalling that it is preparing for all contingencies, including the fracturing of Syria and the complete collapse of the state.

The question for the US will be whether aiding an enemy of the Turkish state will impinge dramatically on their relationship with a NATO ally.

Foreign efforts

There have been numerous efforts by both the US and European partners to engage the PYD in discussions with a wider pan-Syrian opposition to help prevent this, but these have proven to be largely unsuccessful. The PYD has resisted cooperating with the Syrian opposition, although it has made clear that it does not seek to establish an independent state.

Instead, it has sought to reach agreement with neighbouring Turkey; viewing Ankara as the main hindrance to the group's wider acceptance in the international community. Ankara remains wary of the PYD's gains and has built much of its Syria policy around preventing the empowerment of the Syrian Kurds.

However, Turkey's options for altering US policy are limited without a direct military intervention. The eyes of Western states are on what happens next in newly controlled territory. The PYD claims that its governance mode will be one of a laissez-faire administration, devolving as much autonomy to local councils as is needed to govern, while a central authority in Qamishli - the PYD's de-facto capital - will retain control of macro economic and defence policy.

Therefore, if political settlements and agreements can be reached with the various ethnic constituencies of Tal Abyad, then it will go to some length to show that the PYD is an actor that can be trusted to live up to its promises for multiethnic inclusion and peaceful governance.

However, should it emerge that gerrymandering and ethnic politics colour the PYD's governance in newly taken areas, then not only will it continue to place the PYD under suspicion as an ethnocentric actor, but also threaten further instability.

The US' military first strategy suggests continued support for the YPG, particularly now that they have proved themselves capable of taking territory. But it leaves much undone, openly supporting the YPG will do little to heal the wounds of a broken nation, and may even break it further. But ISIL has to be defeated first if there is to be any healing, and to achieve the narrow objective put forward of degrading ISIL, support for the PYD is a good option from the range of poor solutions available.

A YPG-led strategy should not, however, distract from the overarching multilateral efforts to ensure that Bashar al-Assad is removed from power, and that Syria's competing mosaic of factions are finally brought into some form of cohesive, relevant opposition.

Syria's Kurds may not share these concerns of course, and focus simply on building their own institutions, much to the chagrin of Turkey and the international community. But this eventuality is the inevitable price of avoiding the far higher price of a military intervention that no Western or regional government is currently prepared to undertake.

Michael Stephens is a research fellow for Middle East studies and head of the Royal United Services Institute (RUSI) in Qatar.

Aaron Stein is a non-resident fellow with the Rafik Hariri Center for the Middle East, a doctoral fellow at the Geneva Center for Security Policy, and an associate fellow at the Royal United Services Institute in London.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.