Between 2003 and 2011, dozens of Muslims from Europe and the United States traveled to Iraq to fight Western forces. Some of them supported al Qaeda after it established a local affiliate in 2004 (a group known as al Qaeda in Iraq, which became the precursor to ISIS), and many grew more radicalized during their stay. In 2005, then CIA Director Porter Goss warned the Senate Select Committee on Intelligence that “Islamic extremists are exploiting the Iraqi conflict to recruit new anti-U.S. jihadists.”
Yet despite such grim predictions, jihadist veterans of Iraq failed to perpetrate successful terrorist acts in the West. A few cases bore indirect evidence of a link to the conflict, including a bungled June 2007 strike on the Glasgow airport; investigators found that the attackers’ cell phones contained the numbers of several operatives linked to al Qaeda in Iraq. But even in that case, U.S. officials ultimately judged the plot to be “al Qaeda–related, rather than al Qaeda–directed.”
Syria and Iraq today are likely to echo this historical record. For one, many foreign volunteers will die in combat. The ferocity of the fighting in Syria and now Iraq—as the radicals battle the two countries’ governments, the Syrian mainstream opposition, and, increasingly, one another—exceeds that of other recent conflicts. Researchers believe that the death toll among foreign volunteers in Syria has already surpassed that of the Iraq war, in which about five percent of all Western fighters are thought to have died. Of those who do survive, many will never return home, fearing arrest or choosing to wage jihad in other foreign lands. One European intelligence official estimated in an interview with us in May 2014 that from ten to 20 percent of foreign combatants have no plans to come back to their former countries of residence. (The official requested to remain anonymous because he was not authorized to discuss sensitive information.)
Furthermore, the Islamist groups active in Syria and Iraq, including ISIS, are not especially interested in attacking Europe or the United States.