Armed Iraqi tribesmen on the back of a truck on a road north of Ramadi, on May 18, 2013
Beirut (AFP) - Wearing a white headscarf and a traditional black cloak, the Iraqi tribal sheikh addressed his peers: "We're all in the same boat, the (Islamic) State is our state."
"We say to our families that our swords and those of our brothers, the soldiers of the (Islamic) State are directed against the same enemy," he said in a video released by IS, addressing some 30 tribal figures, some clutching Kalashnikovs.
The sheikh from the Iraqi city of Ramadi which fell to IS on May 15 was one of several tribal leaders in Syria and Iraq who have pledged their support for the jihadist group.
IS appears to have recognised the importance of Syria and Iraq's Sunni Arab tribes early on as it seized control of large parts of both countries last year.
Using a combination of promises and threats, IS is working hard to win over the tribes, analysts say, but so far with mixed results.
Both countries are home to tribes from various sects and ethnicities, but IS considers non-Sunnis to be heretics and has confined its outreach to fellow Sunnis.
In Syria, the country's approximately 15 Sunni tribes account for some 15 percent of the population, though many Syrian Sunnis are not affiliated with a tribe.
In Iraq, there are no official numbers, but tribal allegiances are important in many of the country's provinces, particularly in the west and centre, as well as in northern Mosul.
Experts say IS has used a carrot-and-stick approach with Sunni Arab tribes in both countries, playing on local grievances but also exploiting fear.
- Protection, grievances, fear -
Haian Dukhan and Sinan Hawat, authors of a study on IS's relations with eastern Syria's tribes, said three main factors were at play.
Those include "economic benefits and protection... the fear factor, skilfully exploited and mastered by IS," and grievances "which make the tribes accept or tolerate IS in the face of a common enemy."
IS's focus on winning over tribal support follows in the footsteps of Syria's former president Hafez al-Assad, father and predecessor of President Bashar al-Assad.
Under his rule, tribes were "co-opted" with official posts and subsidies and "were part of the formidable populist powers that shored up the regime," Dukhan and Hawat wrote.
In exchange, they backed the government in confrontations with the Islamist Muslim Brotherhood movement and Kurds seeking autonomous rule.
But the relationship withered with the economic opening overseen by Bashar al-Assad, which meant fewer state jobs and rising resentment.
"IS attempted to fill the gap created by the withdrawal of the state. It provided an alternative structure of clientelism and patronage," Dukhan and Hawat wrote.
The extremist group has also made the cost of defiance high.
In 2014, when the Sunni Shaitat tribe rose up against the group, IS slaughtered more than 900 of its members in Deir Ezzor province.
"It subtly invites recruits either to choose the winning horse or die," the study said.
Despite the incentives to join, and the consequences of failing to, Syria's tribes have been divided in response to the group.
"I challenge you to find a clan or a tribe that has pledged allegiance in its entirety to Daesh (IS) or (Al-Qaeda affiliate) Al-Nusra Front or the rebels," Sheikh Nawaf al-Mulhem, a tribal leader and member of parliament from Syria's central Homs province, told AFP.
"There are individuals who support them, but they do not represent the whole tribe," he said.
- Post-invasion resentment -
In Iraq, similar dynamics are at work, with some tribes inclined to support IS because of their anger at being sidelined after the US-led overthrow of former president Saddam Hussein.
The US post-war administration and the Shiite-led governments that have followed "expelled former soldiers from tribes favoured by Saddam, designated them enemies and deprived them of status, salary and social rank," said Hosham Dawod, a French specialist on Iraq's tribes.
"These groups shifted from (Saddam's ideology of) Baathism to radical jihadism and provide the military, security and political base of Daesh," he said, using the Arabic acronym for the group.
Among those who have joined the group is the Albu Ajil tribe, which is accused of participating in the massacre of up to 1,700 mostly Shiite army recruits at Iraq's Camp Speicher last year.
As in Syria however, other tribes have resisted IS, including the Jughaifa.
The tribe refused to turn over 150 people wanted by IS, and its stronghold in Haditha is one of the few areas in Anbar that has not been overrun by the jihadists.
IS has laid siege to the area and directly threatened the Jughaifa in audio recordings.
Saddam Hussein's own tribe is divided between supporters of IS and dissidents like Sheikh Salah Hasan al-Nada, who has been forced to seek refuge in the Kurdish-controlled city of Arbil.
"A tribe could never join Daesh completely. If all the Sunni tribes had joined it, they would have tipped the balance of force in Iraq," Nada said.