As the US-led coalition's war against the Islamic State (IS) enters its second winter, the West's local allies on the ground in Syria and Iraq appear to be gaining momentum. Certainly, progress has been slower than many would like, and the British government's assessment that victory in the group's heartlands may take three years may not be far off the mark. Yet the recent string of victories by local allies across the region indicates the Pentagon's strategy is working, if only slowly.

The successful simultaneous assaults on the Syrian town of al-Hawl and the Iraqi city of Sinjar are evidence of a Pentagon strategy to carve up the vast IS sea of black into a series of disconnected, isolated city states. Like the push by Kurdish peshmerga forces on the road network surrounding Mosul in 2014, taking Sinjar and al-Hawl now places pressure on IS supply lines between their two major urban holdings of Raqqa and Mosul, funneling the group's road traffic to the more vulnerable minor desert roads to the south.

These conquests — like other recent victories by the Syrian Kurdish fighters of the People's Protection Units (YPG) in Kobane, Tal Abyad, Suluk, Ayn Issa, and Hasakah — have only been made possible by the use of massive US air power to shatter IS defenses in advance of ground assaults by the YPG and their Christian and Sunni Arab auxiliary militias, newly renamed the Syrian Democratic Forces (SDF).

Similarly, the wildly successful peshmerga-led assault on Sinjar last week indicates both the strengths and weaknesses of the coalition's approach. After 15 months of IS rule in Sinjar, entailing the massacres of Yazidi civilians and the harvesting of young women as sex slaves on an industrial scale, the long stalemate in the city was finally broken by a wave of sustained airstrikes summoned by US and British special forces on the ground, and the largest single action in the peshmerga's history. This saw the deployment of 7,500 troops, backed by YPG, Yazidi militia, and Kurdistan Workers Party (PKK) allies, against a mere few hundred IS defenders.

Watch the VICE News documentary, Reclaiming Sinjar: Pushing Back the Islamic State:

Such stacking of the odds in the coalition's favor will currently be difficult to replicate in IS' Sunni Arab heartlands, not least due to the current military weakness of the West's few local Sunni Arab allies.

Furthermore, the Sinjar assault was delayed for weeks by bickering between the peshmerga and the YPG over who would claim the glory of liberating the city. The fractious nature of Kurdish politics means the Kurds are divided as much by squabbling among acronyms of their own devising as they are by arbitrary borders imposed from outside. So holding together the rival factions for a common cause will be a difficult undertaking, complicated further by Turkey's ongoing military and diplomatic campaign against both the PKK and the YPG.

'IS will continue to strike Western interests where it can, when it can, whatever Western policymakers decide'

Now the peshmerga have taken Sinjar, with the intention of annexing it to their autonomous Kurdistan region, most of the war aims of the Kurdistan Regional Government (KRG) have been achieved. It is unclear what role, if any, the peshmerga will play in the long-planned and long-delayed campaign to retake Mosul, and the strength and capabilities of the army of Sunni Arabs the Iraqi Kurds are training for this purpose are yet to be determined. It is quite likely that the peshmerga will now play a predominantly defensive role in the conflict, holding their gains from both IS counterattack and — more troublingly for the coalition — from any attempt by Iraq's Shia-led Popular Mobilization Units (PMU) to regain Baghdad's control of both Sinjar and Kirkuk, as seen in the sputtering clashes between the Peshmerga and PMUs for dominance in Tuz Khurmatu.

In building a broad-based coalition against IS, the US has found itself struggling to contain the wildly different policy goals of its allies. The Sunni Arab kingdoms that Washington originally intended to be the face of the conflict have quietly backed out, distracted by what they see as a more pressing challenge, the war in Yemen, cast as an attempt to contain an increasingly assertive Iran.

The Baghdad government has begun to achieve success against IS, clawing back control of both Tikrit and Baiji, gearing up for an assault on Ramadi, and finally eyeing the road north from Baiji to Mosul for future offensives. Yet the reliance of Baghdad's military campaign on Iranian-funded Shia militias — some of whom are designated terrorist organizations and all of whom display wildly anti-American rhetoric — leads the US to hesitate in backing them to the hilt, a hesitation that then leads to further Shia disenchantment with the US and engagement with Iran and latterly Russia.

Russian attack helicopters fighting non-IS rebels in Western Syria.

Russian navy cruise missiles arc towards Syria.

Perhaps the West's most problematic ally is Turkey. On the one hand, the close proximity of Turkish airbases to the frontlines in northern Syria gives the USAF enhanced capabilities to loiter above the battlefield seeking out IS targets. On the other, Turkey's blind-eye border policy with IS has allowed the group to funnel fighters back and forth with ease, as well as to procure vast amounts of the components needed for the homemade munitions that are the bedrock of their military capabilities.

Perhaps the greatest single obstacle to a successful coalition assault on Raqqa is IS control of Jarablus , the group's last remaining border crossing with Turkey. Without Jarablus, the group will find itself starved of funds from cross-border trade, the ability to replenish its stocks of explosive materials, as well as the ability to get terrorist cells to the West with ease.

Yet the long-standing ambition of the YPG, and now the Syrian Democratic Forces, to seize Jarablus from IS has been blocked by Turkish pressure rather than a lack of military capability. Turkey has repeatedly threatened to respond to any Kurdish-led assault on IS positions in Jarablus with overwhelming military force, instead claiming that a Turkish ground incursion will finally solve the problem, at some unspecified future date.

The bloody IS attack in Paris may finally lead to the resolution of this dispute. Turkey's preference for IS over the Kurds as neighbors is no longer just a Turkish policy issue, but a challenge to the West's ability to protect its citizens at home.

In an attempt to mollify Turkey, the US government's backing of the Kurdish-led SDF with airstrikes — and now with munitions shipments and the presence of US special forces embedded with Kurdish fighters — has been masked with the convenient fiction that American support is going to the Syrian Arab Coalition, a name not once uttered in the entire war until a Pentagon press officer invented it.

This is not a total fiction, however. The Syrian Kurds are well aware that tolerance to their rule in Sunni Arab areas of the country will be limited at very best, and have sought to build up military allies from Sunni Arab populations to handle governance for them in newly-conquered Arab areas. In the desert areas of Hasakah, the role has fallen to the Jaish al-Sanaddid, a confederation of Bedouin fighters drawn from the "royal caste" of the Shammar tribe, whose red and gold flag, derived from the Shammar's 18th century battle flag, now flutters across Hasakah's quiet desert villages.

'This argument stands or falls on the assumption that IS' strategic decisions are valid and sensible'

In the more populated regions of Raqqa now under the SDF's control, the Syrian rebel flag is dominant, carried by groups like the Raqqa Revolutionaries' Brigade, who intend to spearhead the reconquest of their home town, now IS' capital. Long subordinate to the YPG, the Raqqa Revolutionaries' Brigade has been undertaking a concerted recruiting campaign in Arab villages under its control, not all of it voluntary.

In the past few weeks, videos indicate a sudden marked expansion of the group's military capabilities in terms of manpower, vehicles, and weaponry, an expansion certain to continue with deepened Western support. Despite tensions between the Raqqa rebels and the Kurdish PYD party over governance of the mixed Arab and Kurdish city of Tal Abyad, the alliance will likely hold together as long as the prospect of seizing Raqqa and continuing to receive US support exist.

For Syrian rebels not aligned with the Kurds, the prospects look bleak. Russian military intervention in the country may shift the balance in much of the country back in the regime's favor, after a months-long string of rebel victories in the northwest.

Watch the VICE News documentary, **_Jihadists vs. the Assad Regime: Syria's Rebel Advance_**:

While Russian propagandists claim their intervention is focused on IS, and anti-Russian hawks that it solely targets the rebels, the truth is somewhere in between. Russian close air support allowed the Syrian army to achieve a victory against IS at the long-besieged Kweiris air base in rural Aleppo, and will likely lead to the reconquest, soon, of Palmyra, as touted by Russian propaganda. Yet much of their efforts have been focused on the northwest of the country, where IS is non-existent, but which is dominated by a mixed bag of rebels from US-armed moderate groups to al Qaeda factions and every shade of Islamist in between.

In truth, it is unlikely that the US will complain too strongly about a Russian campaign that weakens al Qaeda even at the expense of its own moderate proxies. Al Qaeda's primary Syrian arm, Jabhat al Nusra, effectively sowed the seeds for this turn of events by destroying America's favored groups in northwest Syria, and will reap the results in US acquiescence to Russian airstrikes. Perhaps what will emerge is a quiet division of Syria into American and Russian spheres of influence, with America's proxies, such as the newly-announced New Syrian Army along with the SDF consolidating dominance in the east of the country, and Russian ones in the west. Redoubled efforts to achieve a ceasefire between the rebels and the regime will likely follow, setting aside the western policy aim of deposing Assad for now, and allowing international concentration on the war against IS.

'Blowback is already happening at home, whether the West sends troops or not'

This is a deeply unfair outcome for the Syrian rebels and for the civilians in areas under their control who have suffered far more from indiscriminate regime air attacks than they ever have from IS, but ultimately Western politicians are likely to make the pragmatic calculation that the security of their voters outweigh the world's humanitarian duties to the Syrian people, an assessment both Russia and Assad have spared no efforts to disseminate. If any Western action in Syria will lead to blowback, it is this perceived betrayal, but the response will likely take place in decades rather than years or months.

The 2015 balance sheet looks ominous for IS. The group achieved two major victories this year, in Palmyra and the Homs desert in Syria, and in Ramadi in Iraq. Both gains look likely to be reversed in the coming weeks. On the other side of the ledger, the group has lost thousands of square miles of territory across northeastern Syria and northwest Iraq, including some of its most strategic urban outposts. The proxy war against the group is finally paying dividends, but only slowly. Yet Western policy makers and analysts are increasingly beginning to consider what was previously unthinkable: the prospect of sending western ground troops into direct combat against the group.

The arguments against committing Western troops are manifold, and to a degree valid. It is clear that the Obama administration is keen to kick the perhaps inevitable decision into the long grass, for the next administration to deal with, a result of America's painful original misadventure in Iraq.

Yet the parallels with 2003's invasion and subsequent botched occupation only go so far. The belief that Western ground forces will inevitably lead to local resentment and then resistance are drawn from that experience of unilateral invasion with limited international support and very little local buy-in. Yet the parallels for Western intervention in support of the already existing local allies are closer to 2003's successful deployment of limited US troops in northern Iraq in support of the peshmerga, who then went on to achieve, by regional standards, a stable and functioning state.

Similarly, the recent French experience in Mali showed that the swift recapture of urban centers from lightly-armed jihadist groups is easily achievable, but also that the management of the country without efficient local allies is difficult. Without an internationally-coordinated effort to end the war between the Syrian rebels and Assad, any deployment of Western troops will likely fail. With one, it will likely succeed, if the limited frozen peace achieved in Bosnia or, earlier, Lebanon counts as success.

The second argument is that it is unwise to deploy ground troops because this is what IS wants; the group wants to embroil the West in the Middle East, and it believes that this will lead to their ultimate victory. Yet this argument stands or falls on the assumption that IS' strategic decisions are valid and sensible.

IS wants Western troops to fight them on the ground in the belief that this will hasten the apocalypse and the final battle between Jesus and the false messiah, but it is safe to assume that this turn of events will not factor in the Pentagon's planning. When IS took Mosul last summer, the world avoided striking them as long as possible, until goaded into it by outrages against local civilians designed purely to provoke a response. The response eventually came, and its result, over a year later, has been IS's shrunken ability to hold its ground, its inability to conquer new territory, and its painfully slow but eventually fatal weakening at the hands of aerial bombardment and local allies on the ground. The IS strategic vision, then, is not infallible, and policy decisions derived from its millenarian worldview are not necessarily correct.

The third and final argument against direct deployment of international ground forces is that they will take casualties in the field, and that their intervention will lead to blowback at home. But blowback is already happening at home, whether the West sends troops or not. Whether it is preferable for the inevitable casualties to be suffered by well-equipped troops in the Middle East who can at least defend themselves, or by Western civilians in their home capitals or on vacation is a question for the international community's voters to discuss.

IS will continue to strike Western interests where it can, when it can, whatever Western policymakers decide. The only question is whether to draw out the current strategy and defeat the group within years, or summon up the political will to destroy the group's ability to strike the West within months. IS is at war with the West, whether the West likes it or not. The West will destroy IS as a functioning state whether IS likes it or not. What remains to be decided is when and how.