For years, security experts have warned of the threat from “homegrown terrorists” inspired by al-Qaida’s violent ideology. While American jihadists have not yet pulled off an attack on the scale of 9/11, they were responsible for the Boston Marathon bombings of 2013. Other Western nations have been similarly unfortunate: Homegrown terrorists engineered the Madrid train bombings of 2004 and the London Underground bombings of 2005. And it could get worse as dozens or even hundreds of trained, experienced, radicalized fighters return home from conflicts in the Islamic world.
The Syrian insurgency is the biggest concern. An estimated 11,000 foreign fighters are backing either the government or one of the rebel factions, often the extremist ones. Veterans of Syria’s war have already destabilized nearby nations like Lebanon, Jordan and Iraq. Soon they could turn on the United States and European nations.
Western governments are aware of the danger. Charles Farr, the director of the United Kingdom’s Office for Security and Counter-Terrorism, has called British nationals traveling to Syria to participate in the conflict his nation’s “biggest threat.” The Norwegian Intelligence Agency has warned that dozens of Norwegians fighting in Syria could pose a danger when they come home. In the United States, FBI Director James Comey has warned of a “future 9/11” organized by American veterans of the Syrian conflict.