The rise of Isis over the past year presents a fresh challenge to regional powers while adding a further layer of complexity in a region rapidly spiralling into all-out chaos.
"IS has evolved into a completely different beast over the past year; it is very difficult to define and easy to underestimate," says a security adviser working in the region. "It is now a professional army - heavily armed; using artillery accurately - employing co-ordinated tactics."
US President Barack Obama last week began a campaign of air strikes, hammering Isis positions with laser-guided bombs, as the fighters advanced through the Nineveh plains - carving a path of fear and destruction; a campaign of ethno-religious cleansing which displaced hundreds of thousands of people - to within striking distance of Erbil, in Iraq's Kurdish north.
"Most of the families experienced killing, hunger, sexual assault and the kidnapping of women and girls," says Jihad, a Yazidi from the city of Sinjar, which Isis hit in the past week, abducting women, carrying-out mass executions while driving tens of thousands of people onto the nearby Mt Sinjar. "One of my female relatives, two of her sisters were kidnapped and her children killed by IS. I cannot express my heartbreak."
The US strikes have temporarily halted the Isis advance. However, in neighbouring Syria, where the US has provided only limited support to insurgents seeking to overthrow President Bashar al-Assad, the move was met with indignation. "Do I need to be a Christian, Jew or Yazidi to receive help?" a Syrian opposition activist posted on Facebook.
The US and its allies have provided rebel factions with military support, notably anti-tank weapons, but activists contend the flow of arms has not been sufficient to turn the military tide against the Syrian regime, which relies heavily on its superior airpower. Experts note a lack of cohesive strategy among the range of actors supporting the Syrian insurgents.
France, the US, Saudi Arabia, Turkey and Qatar are all believed to have funnelled arms to rebels; much of it sourced from Libyan stockpiles and moved using Qatari air carriers. Other weapons were sourced from Croatian-controlled stockpiles of Yugoslav arms according to the New York Times. The provision of arms through diffuse channels led to a fracturing of opposition groups while encouraging militias to compete for resources, fracturing insurgent ranks further. Saudi Arabia has attempted to unite major rebel factions, establishing the Islamic Front (IF) with some battlefield success.
Observers note that US support for the Kurds provides the media-savvy Isis with a powerful propaganda opportunity, while playing into its narrative as the representative of Islam standing up to imperial powers that have long determined the fate of the Middle East. Meanwhile, it is unlikely that US strikes will seriously degrade Isis.
"A couple of airstrikes are not going to get them out," says the security adviser. "To dislodge IS you need a co-ordinated ground offensive backed up by air power."
Isis evolved out of al-Qaeda's Syria representative, Jabhat al-Nusra (JN), last year following a power struggle which saw JN's international faction, known as the Muhajireen, swell Isis' ranks. Isis is widely believed to have received support from the Turkish Government - which afforded foreign fighters rear bases on Turkish soil. Turkish intelligence allegedly used the Humanitarian Relief Foundation (IHH), an NGO close to Turkish Prime Minister Recep Tayyip Erdogan, to move weapons into Syria - which has aggressively sought regime change in Damascus.
Private backers in the Gulf have raised vast sums for Isis: The US Department of the Treasury has designated three Kuwaiti Isis financiers as Specially Designated Global Terrorists.
Basic tension emerged within JN as to whether the group would focus exclusively on Syria or, as Isis head Abu Bakr al-Baghdadi desired, take a broader view, linking itself to the global jihad. A report from an Isis operative in Syria, in late 2011, argued that the group should use Syria as a "Tora Bora" from which to expand out, break down the Sykes-Picot borders and eventually take Jerusalem.
Its strategy saw it look to secure assets - oil-fields, grain silos, border zones - from which it could monetise and attract recruits. Isis additionally uses extreme brutality as a tool to sow fear amid its enemies' ranks; one recent video showed Isis militants carrying a rucksack full of heads.
Written off following inter-rebel violence earlier this year, Isis withdrew to its strongholds in Syria's east - seizing weapons, notably from Minagh Air base north of Aleppo, as it withdrew and recalibrated - before rampaging into Iraq, riding a wave of Sunni discontent, and quickly overwhelming Iraqi forces in the deserts of Anbar province.
Bolstered by US-supplied advanced weaponry abandoned as the Iraqi Army scattered, Isis moved on Baghdad, before stalling outside Samarra and subsequently turning its gaze to Kurdish areas of Iraq, while transferring its newly acquired significant military resources throughout Syria and Iraq, bolstering jihadist strength. Ammunition seized in Iraq, for example, was the 5.56mm-calibre rounds fired by M16 assault rifles. More accurate than the Kalashnikov, the seized M16s allow Isis to shoot less, and with greater accuracy.
Isis fighters reportedly punched into the Lebanese town of Arsal and last month overran al-Shaer gas field in Syria's Homs region, making off with 15 tanks and assorted weaponry.
The assault on Kurdish areas of Iraq - Isis factions in Syria are also advancing in a Kurdish-dominated area of Syria, known as Rojava - has forced rival Kurdish factions to unite, further complicating regional dynamics. Peshmerga have conducted coordinated counter-offensives around Sinjar and the Syrian frontier town of Yarubiyeh with both the People's Protection Units (YPG), from Syria's Kurdish northeast, and with fighters from the Kurdistan Workers' Party (PKK) an insurgent group from Turkey. The prospect of an emergent Kurdish unity will trouble Ankara, which has for decades feared the emergence of a coherent Kurdish nationalism on its southern flank. However, distrust between Kurdish factions runs strong and an array of regional powers compete for influence in Kurdish areas.
"There's still much politics beneath the surface that is likely to reemerge once the Isis situation is stabilised," says Tony Badran, research fellow at the Foundation for Defense of Democracies. "I don't know this cooperation between the Kurdish factions heralds a new era of unity. This is a crisis situation and there is a convergence of interests to fend off IS."
Western support for the Kurds is fraught with challenges. "US support for the Kurds will alienate the Turks, the Government in Baghdad and the mainstream opposition in Syria," says Joshua Landis, director of the Centre for Middle East Studies at Oklahoma University. "The US's policy is broken ... We are theoretically arming the opposition to fight both Assad and IS. That is a recipe for disaster."
