IT HAS sparked fear and revulsion across the world, but Islamic State’s ability to attract thousands of foreign fighters to join its cause is perhaps its most terrifying — and mystifying — success.

The emergence overnight of chilling CCTV footage of three British schoolgirls catching a bus to Syria to join the fight has again raised the question of how otherwise comfortable, sometimes middle-class westerners are being convinced to trade their stable lives for a war zone, beheadings, rape and the risk of death themselves. And why has IS succeeded where al-Qaeda couldn’t?

The answer, one expert says, is genius.

RELATED: Footage emerges of British schoolgirls on their way to Syria to join IS

“Baghdadi has demonstrated a good understanding of military tactics but he may have the most creative marketing sense for packaging mass murder since Goebbels,” counterterrorism expert John Miller says of the IS founder Omar al-Baghdadi, a former al-Qaeda leader in Iraq.

More than 3000 westerners are believed to have joined IS, according to counter-extremism think tank the Institute for Strategic Dialogue, with as many as 550 women among them.

In its report, Becoming Mulan? Female Western Migrants to ISIS, released last month, the institute reveals much of this appeal is a result of propaganda, with women particularly attracted to the idea of bagging a bad-boy jihadi husband.

In a piece for the New York Daily News, Miller, Deputy Commissioner of Intelligence & Counterterrorism of the NYPD, said the group’s pitch to potential members was not only evil but effective.

Its use of social media, in particular Twitter, was crucial for recruiting more members and, unlike al-Qaeda appears to have a clear goal rather than a vague mandate of “global jihad,” he said.

‘THE REAL MEDIA GENIUS’

In addition to Twitter, ISIS has a daily newspaper online and a slick monthly magazine, which glorifies their fighters and their battles.

But according to Miller: “The real media genius of ISIS is in the team that produces their videos; at once dark, horrifying and compelling, they are slickly produced with special effects and a movie-maker’s sense of story arc and drama.”

There’s also something else, according to Miller. Baghdadi has given young people a “tangible ... here-and-now place” that recruits can actually travel to, and IS lives this promise “out loud”, on Facebook and Twitter, in online magazines and on YouTube.

“Videos and the magazines paint the Islamic State as a real place, a sovereign nation, where any Muslim can come and live with their family,” Miller says. “If they don’t have a family, no problem, ISIS will find them a wife and a nice place to live.”

AUSTRALIANS LURED

While the majority of westerners come from larger countries such as the US and the UK, Australians have also been convinced to leave and fight with or support the terror group.

According to Foreign Minister Julie Bishop, up to 40 Australian “jihadi brides” are fighting for the Islamic State terror group in Iraq and Syria or supporting them from here.

Ms Bishop told Parliament last week there was an “increasing number of young females” looking to join the conflict.

She raised the case of Gold Coast woman Amira Karroum, killed last year in Syria days after she arrived to join her husband, Yusuf Ali as proof the nation was not immune to the lure of IS propaganda.

“Her death was not martyrdom, it was a tragic, senseless loss. Yet more women are either joining their foreign fighter husbands or apparently seeking to find partners, the so-called jihadi brides are otherwise providing support for terrorist organisations,” Ms Bishop said.

‘BABY, PLEASE COME HOME’

Meanwhile new footage emerged overnight of three British schoolgirls on their way to meet Islamic State militants at the Syrian border.

Friends Amira Abase, 15, Shamima Begum, 15, and Kadiza Sultana, 16 were last seen on February 17 when they boarded a flight from London’s Gatwick Airport headed for Turkey. At the time Scotland Yard said they were intent on joining IS.

The footage shows the trio, who all went to the same school, waiting for 18 hours at Bayrampasa bus station on the European side of Istanbul, which the girls reached by metro from the airport, Milliyet newspaper said, citing police sources.

From there they got on a bus to travel to Sanliurfa, 50km from the Syrian border region controlled by Islamic State militants.

“If you’re watching this, baby, please come home,” said Renu Begum, an older sister of one of the missing girls, Shamima Begum, told the BBC last week. “Mum needs you more than anything in the world. You’re our baby and we just want you home, we want you safe. Just contact anybody let them know that you need help.”

Last year, Austrian teens Samra Kesinovic, 17, and Sabina Selimovic, 15 also made headlines when they left their comfortable homes to marry IS fighters.

They reportedly later said they made a terrible mistake by joining the barbaric lifestyle and wanted to come home.

JIHADI JOHN ‘A DEAD MAN WALKING’

He rose to notoriety as the man believed to have been behind the horrific beheadings of several westerners.

Nicknamed Jihadi John, due to his British accent, he has been unmasked as London man Mohammed Emwazi by the Washington Post and the BBC.

Like many other recruits, the Kuwaiti-born Emwazi is reportedly from a middle class family and earned a degree in computer programming before travelling to Syria in about 2012.

Over the weekend it was revealed Emwazi was being watched by British security service MI5 and pondered suicide in a series of emails, because he felt like “a dead man walking”, The Independent reports.