Nineteen-year-old Shannon Maureen Conley, a nurse’s aide, lived with her mother and father in a modest ranch house in Arvada, Colorado. One day in March, according to court documents, Shannon’s father found her on Skype, talking to a man he did not recognize – a 32-year-old Tunisian Islamic State fighter named Yousr Mouelhi.

Shannon and the fighter asked Mr. Conley for his blessing – they were engaged – and for money for Shannon’s passage to Syria. Mr. Conley, an instructor at a local Catholic college, later told an FBI agent that the two seemed surprised when he denied both requests.

A few weeks later, Shannon Conley tried to board a series of flights that would have brought her to Adana, Turkey, just four hours from Syria’s northern border. From there, she planned to join an Islamic State unit, marry Yousr Mouehli, and support the Jihad as a nurse.

But Conley was arrested at the Denver airport. Last month, she pled guilty to “conspiracy to provide material support to a foreign terrorist organization.”

Shannon Conley’s interactions in the virtual world helped to change her identity. They brought her Al Qaeda’s guidelines for guerilla tactics, and an introduction to a contorted system of Jihadi ethics, and the means to link up with the most violent terrorist group in the world.

More significant is the virtual life of Yousr Mouehli, who, like thousands of other young men, left home to join a war that was not his, perhaps drawn by the images of horrific violence that define Islamic State’s recruitment materials.

It’s a story rooted in the staged acts of brutality that have been minting political capital for organized criminals around the world since the advent of broadband – images that have inspired mass murder from Iraq, to Mexico, to Nigeria – rewriting identities, and leaving thousands dead.

When Khalid Sheikh Mohammed, the mastermind of the 9/11 attacks, decapitated Wall Street Journal reporter Daniel Pearl in Karachi in 2002, he decided to film the act. The video circulated on the internet forums that had connected Al Qaeda to jihadist sympathizers during the 1990s. It dominated the news cycle on American television. But in 2002, broadband was not widely available, and the video failed to boost Al Qaeda’s recruitment. After the killing of Pearl, Osama Bin Laden and his chief ideologue, Ayman al-Zawahiri, discouraged the use of decapitation as a terror tactic, fearing that its brutality would alienate more moderate Islamists.

What happened next illustrated the power of the form of communication Khalid Sheikh Mohammed had unwittingly established – and that Al Qaeda was powerless to stop it.

The U.S. invasion of Iraq made that possible. While Secretary of State Colin Powell was presenting a case for war to the UN Security Council, a convicted rapist named Abu Musab al Zarqawi, who had received a reluctant $200,000 donation from Bin Laden years earlier, was in Iraq organizing a robust force to oppose the coming invasion. Zarqawi’s strategy was to start a sectarian civil war, throw the Americans out, and found an Islamic state in the power vacuum. His tactics – especially his targeted killing of Muslims – rankled Bin Laden.

But Zarqawi, a Jordanian, understood public relations better than Bin Laden. In Afghanistan, in the closing stages of the Soviet war, Zarqawi had been a journalist. He was adroit in media and showed a special affinity for magazines. After the American invasion, he added a new weapon to his media arsenal: the beheading video.

In 2004, a video of Zarqawi beheading American contractor Nick Berg went viral. Widespread broadband access allowed millions of people to view the video online, and with anti-American sentiment at peak fervor around the world, the video became a potent recruiting tool.

The video also changed the identity of Zarqawi’s organization, and its popularity led the group to commit similar acts of violence as a matter of course – against hostages and Iraqi civilians alike. What had been a highly effective terrorist organization was now an international media sensation. Lines of transit through Syria to the Iraqi border were flush with recruits from all corners of the globe. Zarqawi’s organization was so popular in the world of virtual jihad that Bin Laden, after months of negotiations, named it the official Al Qaeda affiliate in Iraq.

Zarqawi was riding high, until he was killed by an American airstrike in 2006, and his organization was nearly destroyed when its moderate Sunni supporters turned on it with the help of American troops.

But Zarqawi’s death didn’t mean an end to the beheadings. In the year he died, Zarqawi’s technique began appearing 7,500 miles away, as a new and horrible weapon in the billion-dollar Mexican drug wars.

Not since the fall of the Mayans and Aztecs had decapitation been a common form of killing in Mexico. Suddenly, it was appearing everywhere – hundreds by the year – and it happened in increasingly theatrical ways.

Once, five severed heads were rolled onto a dance floor. Twelve offending drug dealers were hung upside-down on meat hooks and decapitated, their heads affixed with notes of warning – all caught on film. Others were filmed dying by chainsaw. The largest incident involved 49 people, who were deposited together by a roadside in 2012.

The Mexican Director of Public Safety, Genaro García Luna, said in 2007 that the new wave of beheadings was inspired by Zarqawi’s group, and specifically by the filmed beheading of prisoners in Iraq.

The Al Qaeda-inspired Nigerian group Boko Haram has also taken to filmed beheadings of prisoners in imitation of Zarqawi and his Islamic State successors, who, in their campaign across Syria and Iraq, have decapitated countless soldiers and civilians. They have shared the evidence on Twitter. They have made jokes about it.

What does all of this mean for a Shannon Maureen Conley – and for her betrothed, Yousr Mouehli – whom we know only through a sparse description from an awestruck suburban dad?

∂ßEven if they did not know it, the pair were brought together across 7,000 miles of land and sea by a force that once sought to use a brand of horrific violence as a political tool, and then became defined and fundamentally altered by that violence. The violence, the image of which was projected around the virtual world, took on a life of its own, and proliferated – to Mexico, to Nigeria, and to a modest ranch house in Arvada, Colorado.