When Sir Andrew Parker, the newly appointed head of the U.K. Security Services, gave his first public speech this month in London, he issued a stern warning: Jihadi fighters migrating to Syria are a major security threat to Britain, Europe, and beyond.
It was making the world a more dangerous place. "It's more complicated," Parker told the Royal United Services Institute in Whitehall, the heart of the British government. "More unpredictable."
As the bloody war nears its fourth year, with over 100,000 civilians dead and more than 2 million refugees displaced, it has another, fatal and more realistic consequence: More foreign fighters are being indoctrinated to fight for the Sunni cause, opposing the Shia-backed Bashar al-Assad regime.
"There is good reason to be concerned about Syria," Parker said. "A growing proportion of our casework now has some link to Syria, mostly concerning individuals from the U.K. who have travelled to fight there or who aspire to do so. Al Nusrah and other extremist Sunni groups there aligned with Al Qaeda aspire to attack Western countries."
Parker warned that thousands of Islamic extremists operating in the U.K. see the British public as a legitimate target for attacks. Around 330 people were convicted of terrorism-related offenses in Britain between September 11, 2001 and March 31, 2013. Four British trials have been related to terrorism plots, including an intercepted plan to repeat the July 2005 "7/7" backpack attacks on London that killed 56 and injured 700.
The foreign fighter phenomenon in Syria is clearly a major threat, leaving European governments jittery. It was "one of the things that most worries a number of European government agencies," according to Italian Defense Minister Mario Mauro. The FBI estimates that as many as 700 American Muslims are fighting in Syria.
Syrians and foreigners, full-time and occasional fighters, are thought to number tens of thousands. Estimates range from above 60,000 to below 100,000, according to the online news source ProPublica. As more Sunni foreign fighters converge from across the Muslim world to fight Assad's powerful Shiite allies - Hezbollah and Iran - foreign fighters now make up to 10 percent of the rebels.
The Syrian civil war is the third-largest foreign mujahideen mobilization, following the gathering in Afghanistan in the 1980s to rid the country of Soviet invaders and Iraq in the past decade to torment the American occupiers. There are more foreign fighters in Syria than took part in the wars in Somalia, Afghanistan, or Yemen.
The accumulation of fighters has happened quickly. "The mobilization has been stunningly rapid," says the ProPublica report. "What took six years to build in Iraq at the height of the U.S. occupation may have accumulated inside Syria in less than half that time." Matthew G. Olsen, director of the National Counterterrorism Center, told the Aspen Security Forum in July that Syria has become the predominant jihadist battlefield of the world.
"There are individuals traveling to Syria, becoming further radicalized, becoming trained and then returning as part of a global jihadist movement to Western Europe and, potentially, to the United States," Olsen said. Intelligence estimates the number of fighters from North America, Australia, and Europe who went to Syria to fight to be somewhere around 600 - about 10 percent of the total number of foreign fighters in the country - the others coming mostly from the Middle East and North Africa.
It is easy for Syria to become the new land of jihad. The Turkish border with Syria is porous and hundreds cross overland to join rebel battalions in Aleppo or Idlib. Turkey and Syria are easily accessible from major European airports. The Internet - including seductive Facebook pages and recruiting sites - makes it tantalizing for young Muslim men who want to help the suffering people of Syria.
Once there, they are vulnerable to the increasingly radical Sunni groups that are flooding Northern Syria. And once they return home, the concern is that they have smuggled their newly learned terror skills into the West and can be expected to use them there.
"The global jihad has prioritized the Syrian conflict as its principal front," said a top Spanish intelligence official. The worry is that the experience of Western jihadists "could serve as preparation, as training to return to European countries and carry out attacks at home."
Some social scientists, such as Thomas Hegghammer from the Norwegian Defense Research Establishment, maintain the number of foreign fighters who turn to terror is small in relation to the number who go to fight.
"But numbers are not the problem," argues Robert Danin, from the Council on Foreign Relations. "These fighters go to a place like Syria where they are indoctrinated, exposed to ideology, and then gain expertise. They build networks that they are a part of. I do think this is a tremendous danger."
With Syria on its way to becoming a failed state, there is more chance for it to become a breeding ground for radicals. Danin says it is important to observe who is pouring money into Syria - Saudi Arabia, Qatar, and the Gulf - and to see the large numbers who are genuinely ideologically committed.
"You have some people who want to fight Assad," he said. Some, attracted to the better funded, better equipped radical groups, are ripe for indoctrination. "That makes them more dangerous when they return to their home countries."
An important aspect of the lethal mix of motivations and opportunities is that many foreign fighters are Muslims either born or raised in European or North American countries and who have grown up with an acute sense of alienation, particularly in France, Germany, and Britain.
In France, for instance, Muslims are discriminated against in the labor market, in the workplace, in the search for housing, and they are pushed to live on the margins or outskirts - the banlieues - of major cities. In these circumstances, fighting in Syria represents not only a chance for young disaffected Muslims to defend their faith, but to elevate their status from angry, dispossessed outsiders to romantic freedom fighters.
"People who come back from Syria to their mundane lives in the West.... I worry about this," Danin said. "They are battle tested, they come back with issues and concerns and they are vulnerable to being manipulated. They are trained and equipped to fight. They become trained killers who are exposed to a certain and clear view of the world, and they come back to a very confused world."
In the wake of the failed U.S.-led intervention in Syria last September, opposition fighters, in particular the Free Syrian Army, feel demoralized and abandoned by the West. This leaves a vacuum that is filled by more radical groups: the Islamic State of Syria and Jabhat al-Nusrah, both of which seek to establish a caliphate.
Since November 2001, al-Nusrah Front - an affiliate of Al Qaeda in Iraq (AQI) - has claimed responsibility for nearly 600 hundred attacks in major city centers across Syria in which civilians have been injured or killed, according to the U.S. State Department. AQI has also sent money, people, and material from Iraq to Syria to attack Syrian forces.
"I believe they are a real threat," said Andrew Tabler from the Washington Institute for Near East Policy. "The convergence of Assad and Hezbollah is catnip to Sunni militias who are flying in in unprecedented numbers to fight. This happened in Iraq, but in Syria it is multilayered. There is the historical significance of Syria. And for Europeans, it is easy to reach. It's not like getting to Afghanistan. You can fly to Turkey in a few hours."
Last month, Spanish police stormed a hillside ghetto in Ceuta, a Spanish territory in North Africa, where Wahhabi - Muslims who wish to return to the earliest sources of the Koran - were living and arrested an extremist ring charged with sending 50 fighters to Syria.
In France, which suffered a series of deadly terrorist attacks in the 1990s, there is also growing concern. French sources say that between 2001 and 2010, 50 jihadists went from France to Afghanistan were identified. With Syria they have identified 135 jihadists - in a single year. "It has been very fast and strong," said one French counterterrorism official.
The statistics are even more troubling in Belgium, one-sixth the size of France, where between 100 and 300 jihadists from the country's extremist enclaves have traveled to Syria. "The question is," Tabler ponders. "What do they do when they get home?"