The biggest misconception about ISIS is that it is irrational and insane, according to film-maker and former war correspondent Sebastian Junger.
In his latest documentary Hell On Earth: The Fall Of Syria And The Rise Of ISIS, which airs on the National Geographic Channel in Singapore on Thursday, the acclaimed writer and documentarian tries to unravel what he calls "the greatest tragedy of this generation" - the conflict in Syria and how it fuelled the militant jihadist group ISIS, or Islamic State in Iraq and Syria.
Speaking to the press in Los Angeles earlier this year, the 55-year-old - who was behind the Oscar-nominated Afghan war documentary Restrepo (2010) and the best-selling non-fiction book The Perfect Storm (1997) - tells The Straits Times: "I would say that the biggest misconception is that ISIS is crazy. It's completely rational."
His co-director on the film, British documentarian Nick Quested, 47, adds that "in many ways, the fundamental driving force of the Islamic State isn't Islam - Islam is kind of a marketing tool to attract their soldiers".
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He adds: "As soon as you say, 'It's Islam and we're going to go fight the infidels', it's much more attractive.
"It has metastasised online into this sort of global jihad, but I don't think that was the initial intention. The initial intention was personal revenge and enrichment."
The film-makers' goal was "to explain why Syrian society fell apart", Junger says.
"Tunisia worked pretty well. Libya, obviously, was pretty rough, but it seems to be stabilising. Syria has completely fallen apart and something like 400,000 people have died. It's an extraordinary number. You're starting to get up into a kind of Rwanda-level of violence," he says, referring to the 1994 genocide of up to 800,000 people in the East African nation.
The movie argues that the evolution of ISIS was in some ways a logical response to the chaos prompted by the invasion of Iraq in 2003 by the United States and its allies.
"I was in Afghanistan a lot, but I refused to cover Iraq because I was against the invasion," says Junger, who retired from war reporting after his Restrepo co-director - British photojournalist Tim Hetherington - was killed while covering the Libyan conflict in 2011.
"When we invaded Iraq, we introduced an enormous amount of violence to that society. We backed a Shia-dominated government that waged a kind of war against the Sunni population which, as all humans will, eventually started to defend itself.
"They have no political power, no way to defend themselves physically. There are Shia death squads killing them.
"So in that environment, if an organisation that's ruthless, effective and violent, such as ISIS, comes along and says, 'We will protect you, just sign on and we'll protect the Sunni of northern Iraq and eventually Syria', that looks like a good deal in those circumstances."
When it comes to ISIS' propensity for violence, he again emphasises that it is a mistake to think this is anything other than calculated.
"These are rational processes, these people are not psychotic. They look like they're psychotic because of the kind of public violence they commit, but another point we make in the film is that all societies have committed public violence.
"The Spanish Inquisition, the lynchings of black men in the American South - that could've all been done privately. It was done publicly for a reason, exactly like the executions and torture by ISIS - to send a message and intimidate the population."
Quested says these tactics - which ISIS was familiar with because it recruited from disenfranchised military and intelligence officials - are "a very efficient way to suppress a people". He adds: "They're very scared very quickly."
But while Hell On Earth interviews government officials and experts, it is not "a policy- heavy film", Junger says.
Instead, drawing from almost 1,000 hours of footage, "mostly shot verite style, on the ground, in Syria and Iraq", it takes a close look at the human face of the conflict.
"We have cameras with a refugee family who managed to escape. It documents their life under ISIS and how they get themselves smuggled out of ISIS territory, eventually get to Turkey and on a boat trying to get to Europe."
Junger hopes this visceral look at their ordeal will boost empathy for Syrian refugees.
"They are such a beautiful, noble, courageous, lovely family. The West can't take everyone in the world, obviously, but it also can't shut everyone out. It has to find some middle ground that's compassionate and realistic, but what I hate is the sort of poisonous rhetoric about the nature of these people.
"One of the many things I'm hoping for with this film is that this family and the work we've done portraying them changes the way people see refugees - particularly people who might be reflexively negative about them."
•Hell On Earth: The Fall Of Syria And The Rise Of ISIS airs on the National Geographic Channel (Singtel TV Channel 201 and StarHub TV Channel 411) on Thursday at 10pm.