![Mideast Iraq Al-Qaeda inspired militants stand with captured Iraqi Army Humvee at a checkpoint belonging to Iraqi Army outside Beiji refinery some 155 miles north of Baghdad, June 19, 2014.](https://api.time.com/wp-content/uploads/2014/06/sunni-militants-iraq.jpg?quality=85&w=2400)
As fighters affiliated with the Islamic State of Iraq and Syria (ISIS) militant group seized Iraq’s biggest oil refinery on Wednesday, the government formally asked the White House to respond to the miltants’ threat with airstrikes. The Obama administration has so far hesitated to do so, troubled by the lack of good intelligence on the ground and uneasy about the impact military force might have on a brewing conflict with deep sectarian overtones — though President Barack Obama announced Thursday the U.S. is sending 300 special forces to Iraq in an advisory, non-combat role.
But there’s another issue worth considering: the threat of violent blowback against the U.S. at home. For the moment, ISIS, which has fighters in Syria and Iraq, is focused on expanding its territory on both sides of the border. But an American attack on ISIS could turn the group’s wrath Westward, and it already has the means to retaliate on American shores.
Between an estimated 10,000 to 11,000 foreign fighters have joined the fight against President Bashar Assad in neighboring Syria, some 3,000 of whom have passports that allow them unfettered access to the U.S. and Europe. Most Westerners fighting in Syria say they want to defeat Assad and build a new nation based on the laws of Islam, but their governments fear they could be radicalized and persuaded to return home to attack Western targets.
While there have been several arrests of Europeans, Australians and Americans accused of fighting with or attempting to fight with terrorist groups in Syria, so far no plots against the West originating in Syria have been discovered. (The gunman accused of killing 4 at a Jewish museum in Brussels on May 24 had recently returned from fighting in Syria, but he appears to have been previously radicalized). But that could change rapidly if the United States attacks ISIS fighters directly: In January, ISIS leader Abu Bakr al-Baghdadi warned “Jews and crusaders” against encouraging more moderate groups to take on his organization in Syria: “Very soon you will be in direct confrontation, Allah permitting.”
ISIS fighters from across Europe are bringing in new recruits via social media, causing great concern. According to security officials from several European nations, about 400 British, 100 American and 700 French combatants, among others, have already joined the fight, turning what some may consider a distant war into an immediate threat at home.
“No one should be in any doubt that what we see in Syria and now in Iraq in terms of ISIS is the most serious threat to Britain’s security that there is today,” Prime Minister David Cameron told journalists Tuesday. “The number of foreign fighters in that area, the number of foreign fighters including those from the UK who could try to return to the UK is a real threat to our country.” Cameron also warned Parliament this week that British fighters in Syria and Iraq pose “a greater threat to the UK than the return of foreign jihadists or fighters from the Afghanistan or Pakistan region.”
And the threat isn’t just to the UK. British citizens, of course, can easily travel to the U.S. There are now volunteers in Syria from almost every country in Europe, according to a recent report by the Soufan Group. In early June, Spanish authorities discovered a cell of Islamist militant recruiters in Melilla who they said had been sending volunteers to join insurgencies from Mali to Syria.
It’s unclear just how many Westerners, if any, joined ISIS on its blitzkrieg through northern Iraq, though at least two Danes and a Frenchman died in ISIS offensives in the north of the country earlier this year. There have been accounts of foreigners among the ISIS troops taking Mosul in last week’s attack, but most were described as having North African, non-Iraqi Arab or Chechen accents. ISIS’s Iraq campaign, which utilized the tactics of conventional war rather than guerilla-style suicide attacks, may have required seasoned jihadis over untrained but committed novices from the West.
In a way, though, that doesn’t matter. ISIS, whose regional ambitions are reflected in its name, does not acknowledge the border that divides the two wings of its campaign. An attack on ISIS targets in Iraq is the same as one on ISIS targets in Syria. If Baghdadi or one of his lieutenants calls for revenge on the West, he is likely to find many willing — and able — volunteers.
Turmoil in Iraq as Extremist Militants Make Gains
![Members of the Iraqi Special Operations Forces take their positions during clashes with the al Qaeda-linked Islamic State of Iraq and the Levant (ISIL) in the city of Ramadi Members of the Iraqi Special Operations Forces take their positions during clashes with the al Qaeda-linked Islamic State of Iraq and the Syria (ISIS) in the city of Ramadi, June 19.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-35.jpg?quality=75&w=2400)
![Landsat data courtesy of the U.S. Geological Survey shows smoke rising from the Baiji refinery near Tikrit, Iraq A satellite image shows smoke rising from the Baiji refinery near Tikrit, Iraq, June 18.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-34.jpg?quality=75&w=2400)
![Mideast Iraq Al-Qaeda inspired militants stand with captured Iraqi Army Humvee at a checkpoint belonging to Iraqi Army outside Baiji refinery some 155 miles north of Baghdad, June 19.](https://api.time.com/wp-content/uploads/2014/06/sunni-militants-iraq1.jpg?quality=75&w=2400)
![Mehdi Army fighters march during a military-style training in the holy city of Najaf Mehdi Army fighters loyal to Shiite cleric Moqtada al-Sadr march during a military-style training in the holy city of Najaf, June 17.](https://api.time.com/wp-content/uploads/2014/06/mehdi-army-iraq.jpg?quality=75&w=2400)
![TOPSHOTS-IRAQ-UNREST-VOLUNTEERS Newly-recruited Iraqi volunteers, wearing police forces uniforms, take part in a training session on June 17 in the central Shiite city of Karbala.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-27.jpg?quality=75&w=2400)
![Personnel from Kurdish security forces detain man suspected of being militant belonging to ISIL in the outskirts of Kirkuk Personnel from the Kurdish security forces detain a man suspected of being a militant belonging to the al Qaeda-linked Islamic State in Iraq and Syria (ISIS) in the outskirts of Kirkuk June 16.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-31.jpg?quality=75&w=2400)
![APTOPIX Mideast Iraq Shiite tribal fighters raise their weapons and chant slogans against the al-Qaida-inspired Islamic State of Iraq and Syria (ISIS) in Basra, June 16.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-23.jpg?quality=75&w=2400)
![APTOPIX Mideast Iraq Demonstrators chant pro-al-Qaida-inspired Islamic State of Iraq and Syria (ISIS) as they carry al-Qaida flags in front of the provincial government headquarters in Mosul, June 16.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoul-21.jpg?quality=75&w=2400)
![Iraqi security forces fire artillery during clashes with Sunni militant group Islamic State of Iraq and the Levant in Jurf al-Sakhar Iraqi security forces fire artillery during clashes with Sunni militant group Islamic State of Iraq and Syria (ISIS) in Jurf al-Sakhar June 14.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-25.jpg?quality=75&w=2400)
![An Iraqi security forces member with his weapon takes position as people, who fled from the violence in Mosul, arrive at a camp for internally displaced people on the outskirts of Arbil An Iraqi security forces member with his weapon takes position as people, who fled from the violence in Mosul, arrive in their vehicles at a camp for internally displaced people on the outskirts of Erbil in Iraq's Kurdistan region June 14.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-26.jpg?quality=75&w=2400)
![Mideast Iraq People hold posters showing Iran's spiritual leaders Ayatollah Khomeini, while Iraqi Shiite fighters deploy with their weapons in Basra, Iraq's second-largest city, 340 southeast of Baghdad, June 14.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-181.jpg?quality=75&w=2400)
![IRAQ-UNREST Iraqi Shiite men, some of them wearing military fatigues and guns given by the government, raise their weapons as they gather in the Iraqi town of Jdaideh in the Diyala province on June 14, to show their support for the call to arms by Shiite cleric Grand Ayatollah Ali al-Sistani.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-17.jpg?quality=75&w=2400)
![Mideast Iraq Iraqi men board military trucks to join the Iraqi army at the main recruiting center in Baghdad on June 14, after authorities urged Iraqis to help battle insurgents.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-161.jpg?quality=75&w=2400)
![Refugees Flee Iraq After Recent Insugent Attacks Peshmerga military direct traffic at a Kurdish check point on June 14, in Kalak.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-18.jpg?quality=75&w=2400)
![Refugees Flee Iraq After Recent Insugent Attacks Traffic from Mosul queues at a Kurdish Check point on June 14,in Kalak.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-19.jpg?quality=75&w=2400)
![IRAQ-UNREST-DISPLACED Iraqi women gather at a temporary camp set up to shelter civilians fleeing violence in northern Nineveh province in Aski Kalak, 25 miles west of Erbil, on June 13.](https://api.time.com/wp-content/uploads/2014/06/4505450521.jpg?quality=75&w=2400)
![Refugees Flee Iraq After Recent Insugent Attacks Iraqi children carry water to their tent at a temporary displacement camp set up next to a Kurdish checkpoint on June 13 in Kalak.](https://api.time.com/wp-content/uploads/2014/06/4505688401.jpg?quality=75&w=2400)
![IRAQ-UNREST-WEAPONS A Shiite man cleans weapons as he gets ready to defend his Sadr City district in case of an attack by Sunni extremists, on June 13 in Baghdad.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-20.jpg?quality=75&w=2400)
![TOPSHOTS-IRAQ-UNREST An Iraqi soldier bodychecks men as they arrive to volunteer to join the fight against a major offensive by jihadists in northern Iraq on June 13, 2014, at recruiting center in the capital Baghdad.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-14.jpg?quality=75&w=2400)
![IRAQ-UNREST Iraqi policemen dig trenches at checkpoint in the Iraqi town of Taji, at the entrance of Baghdad, on June 13, 2014, as security forces are bolstering defenses in the capital.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-13.jpg?quality=75&w=2400)
![Mideast Iraq Men chant slogans against the al-Qaida breakaway group Islamic State of Iraq and Greater Syria (ISIS), outside of the main army recruiting center to volunteer for military service in Baghdad, June 12, 2014.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil.jpg?quality=75&w=2400)
![Unrest in Mosul An Iraq army vehicle is seen burned by militants in Mosul, on June 12, 2014.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-6.jpg?quality=75&w=2400)
![APTOPIX Mideast Iraq Refugees fleeing from Mosul head to the semi-autonomous northern Kurdish region in Erbil, north of Baghdad, June 12, 2014.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-11.jpg?quality=75&w=2400)
![Families fleeing the violence in the Iraqi city of Mosul arrive at a checkpoint on the outskirts of Arbil Families fleeing the violence in the Iraqi city of Mosul arrive at a checkpoint on the outskirts of Erbil, in Iraq's Kurdistan region June 12, 2014.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-12.jpg?quality=75&w=2400)
![Fighters of the Islamic State of Iraq and the Levant (ISIL) stand guard at a checkpoint in the northern Iraq city of Mosul Fighters of the Islamic State of Iraq and Syria (ISIS) stand guard at a checkpoint in the northern Iraq city of Mosul, June 11, 2014.](https://api.time.com/wp-content/uploads/2014/06/iraq-turmoil-9.jpg?quality=75&w=2400)
![Civilian children stand next to a burnt vehicle during clashes between Iraqi security forces and al Qaeda-linked Islamic State in Iraq and the Levant (ISIL) in the northern Iraq city of Mosul Civilian children stand next to a burnt vehicle during clashes between Iraqi security forces and al Qaeda-linked Islamic State in Iraq and the Levant (ISIL) in the northern Iraq city of Mosul](https://api.time.com/wp-content/uploads/2014/06/rtr3t3ut.jpg?quality=75&w=2400)
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