When Abu Hamza, a former Syrian rebel, agreed to join Isis, he did so assuming he would become a part of the group’s promised Islamist utopia, which has lured foreign jihadists from around the globe.

Instead, he found himself being supervised by an Iraqi emir and receiving orders from shadowy Iraqis who moved in and out of the battlefield in Syria. When Abu Hamza disagreed with fellow commanders at an "Islamic State" meeting last year, he said, he was placed under arrest on the orders of a masked Iraqi man who had sat silently through the proceedings, listening and taking notes.

Abu Hamza, who became the group’s ruler in a small community in Syria, never discovered the Iraqis’ real identities, which were cloaked by code names or simply not revealed. All of the men, however, were former Iraqi officers who had served under Saddam Hussein, including the masked man, who had once worked for an Iraqi intelligence agency and now belonged to the Islamic State’s own shadowy security service, he said.

US Marines chain the head of a statue of Saddam Hussein before pulling it down in Baghdad's al-Fardous square 09 April 2003, while an Iraqi waves the US flag. (Getty Images)

His account, and those of others who have lived with or fought against the Islamic State over the past two years, underscore the pervasive role played by members of Iraq’s former Baathist army in an organisation more typically associated with flamboyant foreign jihadists and the gruesome videos in which they star.

Even with the influx of thousands of foreign fighters, almost all of the leaders of the Islamic State are former Iraqi officers, including the members of its shadowy military and security committees, and the majority of its emirs and princes, according to Iraqis, Syrians and analysts who study the group.

They have brought to the organisation the military expertise and some of the agendas of the former Baathists, as well as the smuggling networks developed to avoid sanctions in the 1990s and which now facilitate the Islamic State’s illicit oil trading.

In Syria, local “emirs” are typically shadowed by a deputy who is Iraqi and makes the real decisions, said Abu Hamza, who fled to Turkey last summer after growing disillusioned with the group. He uses a pseudonym because he fears for his safety.

“All the decision makers are Iraqi, and most of them are former Iraqi officers. The Iraqi officers are in command, and they make the tactics and the battle plans,” he said. “But the Iraqis themselves don’t fight. They put the foreign fighters on the front lines.”

Timeline: The emergence of Isis Show all 40 1 /40 Timeline: The emergence of Isis Timeline: The emergence of Isis 2000 Abu Musab al-Zarqawi (pictured here) forms an al-Qaeda splinter group in Iraq, al-Qa’eda in Iraq. Its brutality from the beginning alienates Iraqis and many al-Qaeda leaders. Timeline: The emergence of Isis 2006 Al-Zarqawi is killed in a U.S. strike. Al-Zarqawi’s successor, Abu Ayyub al-Masri, announces the creation of the Islamic State in Iraq (ISI). Reuters Timeline: The emergence of Isis 2009 Still al-Qaeda-linked ISI claims responsibility for suicide bombings that killed 155 in Baghdad, as well as attacks in August and October killing 240, as President Obama announces troop withdrawal from Iraq in March. Getty Images Timeline: The emergence of Isis 2010 Abu Bakr al-Baghdadi becomes head of ISI, at lowest ebb of Islamist militancy in Iraq, which sees last U.S. combat brigade depart. Timeline: The emergence of Isis 2012 In Syria, protests (pictured here starting in Daree) have morphed into what president Assad labelled a “real war” with emergence of a coalition of forces opposed to Assad’s regime. Syria group Jabhat al-Nusra are among rebel groups who refuse to join, denouncing it as a “conspiracy”. Bombings targeting Shia areas, killing more than 500 people, spark fears of new sectarian conflict. Sunni Muslims stage protests across country against what they see as increasingly marginalisation by Shia-led government. AP Timeline: The emergence of Isis 2013 Al-Baghdadi renames ISI as the Islamic State in Iraq and Syria, or Isis, as the group absorbs Syrian al-Nusra, gaining a foothold in Syria. In response, al-Qaeda chief Ayman al-Zawahiri (Bin Laden’s successor) concerned about Isis’ expansion orders that Isis be dissolved and ISI operations should be confined to Iraq. This order is rejected by al-Baghdadi. AFP Timeline: The emergence of Isis 2014 - January Isis fighters capture the Iraqi cities of Fallujah and Ramadi, giving them base to launch slew of attacks further south. AP Timeline: The emergence of Isis 2014 - June Isis declares itself the Caliphate, calling itself Islamic State (IS). The group captures Mosul, Iraq’s second largest city; Tal Afar, just 93 miles from Syrian border; and the central Iraqi city of Tikrit. These advances sent shockwaves around the world. Timeline: The emergence of Isis 2014 - June Around the same time Isis releases a video calling for western Muslims to join the Caliphate and fight, prompting new evaluations of extremists groups social media understanding. Timeline: The emergence of Isis 2014 - June Isis take Baiji oil fields in Iraq - giving them access to huge amounts of possible revenue. EPA Timeline: The emergence of Isis 2014 - August James Foley is executed by the group as concerns grow for second American prisoner, fellow reporter Steven Sotloff. AP Timeline: The emergence of Isis 2014 - August Obama authorises U.S. airstrikes in Iraq, helping to stall Isis’ along with action by Kurdish forces following the deaths of hundreds of Yazidi people on Mount Sinjar. Timeline: The emergence of Isis 2014 - September Isis release video showing Steven Sotloff’s murder prompting Western speculation his executioner is same man who killed Mr Foley. EPA Timeline: The emergence of Isis 2014 - September Obama tells us that America “will hunt down terrorists who threaten our country” EPA Timeline: The emergence of Isis 2014 - September Isis release a video appearing to show David Haines, who was captured by militants in Syria in 2013, wearing an orange jumpsuit and kneeling in the desert while he reads a pre-prepared script. It later shows what appears to be the aid worker's body. Rex Timeline: The emergence of Isis 2014 - September Peshmerga fighters scrabble to hold positions in the Diyala province (a gateway to Baghdad) as Isis fighters continue to advance on Iraqi capital. AFP Timeline: The emergence of Isis 2014 - October Aid worker Alan Henning is killed. Self-imposed media blackout refuses to show images of him in final moments, instead focuses upon humanitarian care. AP Timeline: The emergence of Isis 2014 - October Isis raise their flag in Kobani, which had been strongly defended by Kurdish troops. The victory goes against hopeful western analysis Isis had overextended itself, while alienating much of the Muslim population through the murder of Henning. Victory causes fresh waves of Kurdish refugees arriving in Turkey. Timeline: The emergence of Isis 2014 - November American hostage, who embarced values of Islam, Peter Kassig and 14 Syrian soldiers are shown meeting the same fate as other captives. But intelligence agencies will be poring over the apparently significant discrepancies between this and previous films. Seramedig.org.uk Timeline: The emergence of Isis 2015 - February Isis has released a video revealing the murder by burning to death of a Jordanian pilot held by the group since the end of December 2014. Reuters Timeline: The emergence of Isis 2015 - February Isis militants have released videos which appear to show the beheading of Japanese hostages Haruna Yukawa and Kenji Goto. Timeline: The emergence of Isis 2015 - February American aid worker, Kayla Mueller was the last American hostage known to be held by Isis. She died, according to her captors, in an airstrike by the Jordanian air force on the city of Raqqa in Syria, though US authorities disputed this. AP Timeline: The emergence of Isis 2015 - February Isis militants have posted a gruesome video online in which they force 21 Egyptian Coptic Christian hostages to kneel on a beach in Libya before beheading them. Egypt vowed to avenge the beheading and launched air strikes on Isis positions. AP Timeline: The emergence of Isis 2015 - February The British Isis militant suspected of appearing in videos showing the beheading of Western hostages has been named in reports as Mohammed Emwazi from London. Rex Features Timeline: The emergence of Isis 2015 - March Isis triple suicide attack has killed more than 100 worshippers and hundreds of others were injured after the group members targeted two mosques in the Yemeni capital of Sanaa. AP Timeline: The emergence of Isis 2015 - April Iraqi forces have claimed victory over Isis in battle for Tikrit and raised the flag in the city. EPA/STR Timeline: The emergence of Isis 2015 - April Isis has claimed responsibility for a suicide bomb attack in Afghanistan that killed at least 35 people queuing to collect their wages and injured 100 more. EPA Timeline: The emergence of Isis 2015 - April Isis’ media arm released a 29-minute video purporting to show militants executing Ethiopian Christians captives. The footage bore the extremist group’s al-Furqan media logo and showed the destruction of churches and desecration of religious symbols. A masked fighter made a statement threatening Christians who did not convert to Islam or pay a special tax. Timeline: The emergence of Isis 2015 - May Abu Bakr al-Baghdadi, the leader of Isis has been "incapacitated" by a spinal injuries sustained in a US air strike in Iraq. He is being treated in a hideout by two doctors from Isis’ stronghold of Mosul who are said to be "strong ideological supporters of the group". Timeline: The emergence of Isis 2015 - May Isis has also claimed responsibility for killing 300 of Yazidi captives, including women, children and elderly people in Iraq AP Timeline: The emergence of Isis 2015 - May Isis attack on Prophet Mohamed cartoon contest in Texas was its first action on US soil. Two gunmen were shot and killed after launching the attack at the exhibition. Elton Simpson and Nadir Soofi have been named as the attackers at the Curtis Culwell Centre arena in Garland. Timeline: The emergence of Isis 2015 - May Isis’s deputy leader, Abu Alaa Afri, a former physics teacher who was thought to have taken charge of the deadly terrorist group, has been killed in a US-led coalition airstrike. Timeline: The emergence of Isis 2015 - May US special forces have killed a senior Isis leader named as Abu Sayyaf in an operation aiming to capture him and his wife in Syria. Getty Images Timeline: The emergence of Isis 2015 - May Iran-backed militias are sent to Ramadi by the Iraqi government to fight Isis militants who completed their capture of the city. Government soldiers and civilians were reportedly massacred by extremists as they took control and the army fled. Charred bodies were left littering the city streets as troops clung on to trucks speeding away from the city. Ramadi is the latest government stronghold to fall to the so-called Islamic State, despite air strikes by a US-led international coalition aiming to stop its advance in Iraq and Syria. AFP Timeline: The emergence of Isis 2015 - May Isis rounded up civilians trapped in Palmyra and forced them to watch 20 people being executed in the historic city’s ancient amphitheatre. The Unesco World Heritage site was overrun by militants, threatening the future of 2,000 year-old monuments and ruins. Thousands of Palmyra’s residents fled but many are still living within the city walls, while the UN human rights office in Geneva said it had received reports of Syrian government forces preventing people from leaving until they retreated from the city. Getty Timeline: The emergence of Isis 2015 - May A group of Isis-affiliated fighters have captured a key airport in central Libya. The militants took control of the al-Qardabiya airbase in Sirte after a local militia tasked with defending the facility withdrew from their positions. Affiliates of Isis, already control large parts of Sirte, the birthplace of former Libyan leader Muammar Gaddafi and a former stronghold of his supporters. Timeline: The emergence of Isis 2015 - June The US Air Force has destroyed an Isis stronghold after an extremist let slip their location on social media. According the Air Force Times, General Herbert "Hawk" Carlisle, commander of Air Combat Command, said that Airmen at Hulburt Field, Florida, used images shared by jihadists to track the location of their headquarters before destroying it in an airstrike. Reuters Timeline: The emergence of Isis 2015 - June Kurdish forces captured a key military base in a significant victory in Raqqa as well as town of Tell Abyad. YPG fighters, backed by US-led airstrikes and other rebels, consolidated their gains, when they seized the key town on the Syria-Turkey border. They are now just 30 miles to the north of Raqqa and have cut off a major supply route deep inside Isis-held territory. Ahmet Silk/Getty Timeline: The emergence of Isis 2015 - June Isis has released gruesome footage claiming to show the murder of more than a dozen men by drowning, decapitation and using a rocket-propelled grenade as it seeks to boost morale among its fanatical supporters. Timeline: The emergence of Isis 2015 - June Isis has begun carrying out its threat to destroy structures in the ancient Syrian city of Palmyra, blowing up at least two monuments at the Unesco-protected site as Syrian government troops made advances on the Islamist’s positions. AFP

The public profile of the foreign jihadists frequently obscures the Islamic State’s roots in the bloody recent history of Iraq, its brutal excesses as much a symptom as a cause of the country’s woes.

The raw cruelty of Hussein’s Baathist regime, the disbandment of the Iraqi army after the US-led invasion in 2003, the subsequent insurgency and the marginalization of Sunni Iraqis by the Shia-dominated government all are intertwined with the Islamic State’s ascent, said Hassan Hassan, a Dubai-based analyst and co-author of the book Isis: Inside the Army of Terror.

“A lot of people think of the Islamic State as a terrorist group, and it’s not useful,” Hassan said. “It is a terrorist group, but it is more than that. It is a homegrown Iraqi insurgency, and it is organic to Iraq.”

The de-Baathification law promulgated by L.­ Paul Bremer, Iraq’s American ruler in 2003, has long been identified as one of the contributors to the original insurgency. At a stroke, 400,000 members of the defeated Iraqi army were barred from government employment, denied pensions — and also allowed to keep their guns.

Saddam Hussein's Ba'ath party was banned after the 2003 US invasion and members banned from public office and education, removing thousands of people from their jobs (GETTY)

The US military failed in the early years to recognise the role the disbanded Baathist officers would eventually come to play in the extremist group, eclipsing the foreign fighters whom American officials preferred to blame, said Colonel Joel Rayburn, a senior fellow at the National Defense University who served as an adviser to top generals in Iraq and describes the links between Baathists and the Islamic State in his book, Iraq After America.

The US military always knew that the former Baathist officers had joined other insurgent groups and were giving tactical support to the Al Qaeda in Iraq affiliate, the precursor to the Islamic State, he said. But American officials didn't anticipate that they would become not only adjuncts to al-Qaeda, but core members of the jihadist group.

“We might have been able to come up with ways to head off the fusion, the completion of the Iraqisation process,” he said. The former officers were probably not reconcilable, “but it was the labeling of them as irrelevant that was the mistake.”

Under the leadership of Abu Bakr al-Baghdadi, the Islamic State’s self-proclaimed caliph, the former officers became more than relevant. They were instrumental in the group’s rebirth from the defeats inflicted on insurgents by the US military, which is now back in Iraq bombing many of the same men it had already fought twice before.

Abu Bakr al-Baghdadi is one of the few senior Isis officials not to be a former Iraqi official

At first glance, the secularist dogma of Hussein’s tyrannical Baath Party seems at odds with the Islamic State’s harsh interpretation of the Islamic laws it purports to uphold.

But the two creeds broadly overlap in several regards, especially their reliance on fear to secure the submission of the people under the group’s rule. Two decades ago, the elaborate and cruel forms of torture perpetrated by Hussein dominated the discourse about Iraq, much as the Islamic State’s harsh punishments do today.

Like the Islamic State, Hussein’s Baath Party also regarded itself as a transnational movement, forming branches in countries across the Middle East and running training camps for foreign volunteers from across the Arab world.

By the time US troops invaded in 2003, Hussein had begun to tilt toward a more religious approach to governance, making the transition from Baathist to Islamist ideology less improbable for some of the disenfranchised Iraqi officers, said Ahmed S. Hashim, a professor who is researching the ties at Singapore’s Nanyang Technological University.

The Iraqi Army was rebuilt after the 2003 Iraq invasion, leading many disaffected commanders to flee (Reuters)

With the launch of the Iraqi dictator’s Faith Campaign in 1994, strict Islamic precepts were introduced. The words “God is Great” were inscribed on the Iraqi flag. Amputations were decreed for theft. Former Baathist officers recall friends who suddenly stopped drinking, started praying and embraced the deeply conservative form of Islam known as Salafism in the years preceding the US invasion.

In the last two years of Hussein’s rule, a campaign of beheadings, mainly targeting women suspected of prostitution and carried out by his elite Fedayeen unit, killed more than 200 people, human rights groups reported at the time.

The brutality deployed by the Islamic State today recalls the bloodthirstiness of some of those Fedayeen, said Hassan. Promotional videos from the Hussein era include scenes resembling those broadcast today by the Islamic State, showing the Fedayeen training, marching in black masks, practicing the art of decapitation and in one instance eating a live dog.

Some of those Baathists became early recruits to the al-Qaeda affiliate established by Abu Musab al-Zarqawi, the Palestinian Jordanian fighter who is regarded as the progenitor of the current Islamic State, said Hisham al Hashemi, an Iraqi analyst who advises the Iraqi government and has relatives who served in the Iraqi military under Hussein. Other Iraqis were radicalised at Camp Bucca, the American prison in southern Iraq where thousands of ordinary citizens were detained and intermingled with jihadists.

Abu Musab al-Zarqawi recruited Baathists

Zarqawi kept the former Baathists at a distance, because he distrusted their secular outlook, according to Hashim, the professor.

It was under the watch of the current Islamic State leader, Abu Bakr al-Baghdadi, that the recruitment of former Baathist officers became a deliberate strategy, according to analysts and former officers.

Tasked with rebuilding the greatly weakened insurgent organization after 2010, Baghdadi embarked on an aggressive campaign to woo the former officers, drawing on the vast pool of men who had either remained unemployed or had joined other, less extremist insurgent groups.

Some of them had fought against al-Qaeda after changing sides and aligning with the American-backed Awakening movement during the surge of troops in 2007. When US troops withdrew and the Iraqi government abandoned the Awakening fighters, the Islamic State was the only surviving option for those who felt betrayed and wanted to change sides again, said Brian Fishman, who researched the group in Iraq for West Point’s Combating Terrorism Center and is now a fellow with the New America Foundation.

Baghdadi’s effort was further aided by a new round of de-Baathification launched after US troops left in 2011 by then Prime Minister Nouri al-Maliki, who set about firing even those officers who had been rehabilitated by the American military.

Among them was Brigadier General Hassan Dulaimi, a former intelligence officer in the old Iraqi army who was recruited back into service by US troops in 2006, as a police commander in Ramadi, the capital of the long restive province of Anbar.

Brigadier General Hassan Dulaimi was dismissed as the police commander in Ramadi, which is now partly controlled by Isis (Mohammed Jalil/EPA)

Within months of the American departure, he was dismissed, he said, losing his salary and his pension, along with 124 other officers who had served alongside the Americans.

“The crisis of Isis didn't happen by chance,” Dulaimi said in an interview in Baghdad, using an acronym for the Islamic State. “It was the result of an accumulation of problems created by the Americans and the [Iraqi] government.”

He cited the case of a close friend, a former intelligence officer in Baghdad who was fired in 2003 and struggled for many years to make a living. He now serves as the Islamic State’s wali, or leader, in the Anbar town of Hit, Dulaimi said.

“I last saw him in 2009. He complained that he was very poor. He is an old friend, so I gave him some money,” he recalled. “He was fixable. If someone had given him a job and a salary, he wouldn't have joined the Islamic State.

“There are hundreds, thousands like him,” he added. “The people in charge of military operations in the Islamic State were the best officers in the former Iraqi army, and that is why the Islamic State beats us in intelligence and on the battlefield.”

The Islamic State’s seizure of territory was also smoothed by the Maliki government’s broader persecution of the Sunni minority, which intensified after US troops withdrew and left many ordinary Sunnis willing to welcome the extremists as an alternative to the often brutal Iraqi security forces.

Iraqi Prime Minister Nouri al-Maliki was accused of persecuting Iraq's Sunni minority (AFP)

But it was the influx of Baathist officers into the ranks of the Islamic State itself that propelled its fresh military victories, said Hashem. By 2013, Baghdadi had surrounded himself with former officers, who oversaw the Islamic State’s expansion in Syria and drove the offensives in Iraq.

Some of Baghdadi’s closest aides, including Abu Muslim al-Turkmani, his deputy in Iraq, and Abu Ayman al-Iraqi, one of his top military commanders in Syria, both of them former Iraqi officers, have since reportedly been killed — though Dulaimi suspects that many feign their own deaths in order to evade detection, making its current leadership difficult to discern.

Any gaps however are filled by former officers, sustaining the Iraqi influence at the group’s core, even as its ranks are swelled by arriving foreigners, said Hassan.

Fearing infiltration and spies, the leadership insulates itself from the foreign fighters and the regular Syrian and Iraqi fighters through elaborate networks of intermediaries frequently drawn from the old Iraqi intelligence agencies, he said.

“They introduced the Baathist mind-set of secrecy as well as its skills,” he said.

The masked man who ordered the detention of Abu Hamza was one of a group of feared security officers who circulate within the Islamic State, monitoring its members for signs of dissent, the Syrian recalled.

“They are the eyes and ears of Daesh’s security, and they are very powerful,” he said, using an Arabic acronym for the Islamic State.

Saddam Hussein's former military leaders are operating in the highest levels of Isis (GETTY IMAGES)

Abu Hamza was released from jail after agreeing to fall into line with the other commanders, he said. But the experience contributed to his disillusionment with the group.

The foreign fighters he served alongside were “good Muslims,” he said. But he is less sure about the Iraqi leaders.

“They pray and they fast and you can’t be an emir without praying, but inside I don’t think they believe it much,” he said. “The Baathists are using Daesh. They don’t care about Baathism or even Saddam.

“They just want power. They are used to being in power, and they want it back.”

Whether the former Baathists adhere to the Islamic State’s ideology is a matter of debate. Hashim suspects many of them do not.

“One could still argue that it’s a tactical alliance,” he said. “A lot of these Baathists are not interested in ISIS running Iraq. They want to run Iraq. A lot of them view the jihadists with this Leninist mind-set that they’re useful idiots who we can use to rise to power.”

Rayburn questions whether even some of the foreign volunteers realise the extent to which they are being drawn into Iraq’s morass. Some of the fiercest battles being waged today in Iraq are for control of communities and neighborhoods that have been hotly contested among Iraqis for years, before the extremists appeared.

“You have fighters coming from across the globe to fight these local political battles that the global jihad can’t possibly have a stake in.”

The Iraq War: A timeline Show all 16 1 /16 The Iraq War: A timeline The Iraq War: A timeline 11 September 2001 Terrorists belonging to al-Qaeda use hijacked aeroplanes to kill 2,996 people in attacks on the east coast of the US. AP The Iraq War: A timeline 12 September 2001 Tony Blair promises George W Bush that the UK will support the US, whatever the President decides to do. AFP/Getty Images The Iraq War: A timeline 25 March 2002 Jack Straw, Foreign Secretary, warns Blair that invading Iraq would be legally dubious. Getty Images The Iraq War: A timeline June 2002 Tony Blair asks defence officials to outline options for UK participation in military action against Iraq. afp/getty images The Iraq War: A timeline 24 September 2002 The government publishes a dossier about the threat from Iraq’s weapons of mass destruction. A foreword by Tony Blair states that Saddam Hussein’s “military planning allows for some of the WMD to be ready within 45 minutes of an order to use them”. It is subsequently alleged that this dossier was “sexed up” for political reasons. Getty The Iraq War: A timeline 2 October 2002 Congress authorises President Bush to use military force against Iraq. Getty The Iraq War: A timeline 8 November 2002 UN Security Council passes resolution 1441, insisting that weapons inspectors be allowed back into Iraq and calling on the regime to give up its WMD or face the consequences. Simon Walker/AP The Iraq War: A timeline 18 July 2003 David Kelly, an expert in biological warfare, is found dead after being named as the source of quotations used by the BBC’s Andrew Gilligan to suggest that the dossier of September 2002 had been “sexed up”. Lord Hutton is appointed to chair a judicial inquiry into his death. GETTY IMAGES The Iraq War: A timeline 13 December 2003 Saddam Hussein is captured near Tikrit, after nine months in hiding. REUTERS The Iraq War: A timeline 2 March 2004 Bombings in Baghdad and Karbala kill nearly 200 people: the worst attacks since the fall of Saddam. Getty Images The Iraq War: A timeline 14 September 2005 Bombs in Baghdad kill 160 people and injure more than 500. EPA The Iraq War: A timeline 30 December 2005 Saddam Hussein is executed. Getty Images The Iraq War: A timeline 28 May 2009 The last British combat troops leave Iraq. Getty Images The Iraq War: A timeline 24 November 2009 The Chilcot inquiry holds its first public hearing. Getty The Iraq War: A timeline 2 February 2011 The Chilcot inquiry holds its final public hearing. AFP/Getty Images The Iraq War: A timeline 21 January 2015 Sir John Chilcot confirms that his report will not be published before the general election in May 2015. Getty Images

Former Baathist officers who served alongside some of those now fighting with the Islamic State believe it is the other way around. Rather than the Baathists using the jihadists to return to power, it is the jihadists who have exploited the desperation of the disbanded officers, according to a former general who commanded Iraqi troops during the Iraqi invasion of Kuwait in 1990 and the US invasion of Iraq in 2003. He spoke on the condition of anonymity because he fears for his safety in Irbil, the capital of the northern Iraqi region of Kurdistan, where he now resides.

The ex-Baathists could be lured away, if they were offered alternatives and hope for the future, he said.

“The Americans bear the biggest responsibility. When they dismantled the army what did they expect those men to do?” he asked. “They were out in the cold with nothing to do and there was only one way out for them to put food on the table.”

When US officials demobilised the Baathist army, “they didn't de-Baathify people’s minds, they just took away their jobs,” he said.

There are former Baathists with other insurgent groups who might be persuaded to switch sides, said Hassan, citing the example of the Army of the Men of the Naqshbandi Order, usually referred to by its Arabic acronym JRTN. They welcomed the Islamic State during its sweep through northern Iraq last summer, but the groups have since fallen out.

But most of the Baathists who actually joined the Islamic State are now likely to have themselves become radicalised, either in prison or on the battlefield, he said.

“Even if you didn't walk in with that vision you might walk out with it, after five years of hard fighting,” said Fishman, of the New America Foundation. “They have been through brutal things that are going to shape their vision in a really dramatic way.”