The estimates vary as to how many citizens of Western countries have traveled to the Middle East with the intention of joining with Islamic State fighters. A July estimate suggested that as many as 10,000 foreigners could be in Syria fighting alongside anti-Assad rebels, including the Islamic State. Another 3,000 ISIS militants were believed to hold European or other Western passports, and another 100 were believed to be American citizens.
Western intelligence officials have surely been losing sleep over the nature of the threat posed by Western citizens, trained in Jihad, but carrying identification which allows them to easily transit into and out of the West. In July, it was revealed that Moner Mohammad Abusalha, an American who fought alongside ISIS in Syria and executed a suicide attack on pro-Assad forces in May, traveled freely to and from the United States undetected before carrying out his mission.
For some, it is hard to comprehend the urge to leave the West and to live under and fight for Sharia law. That is why this interview with the British national, Abu Rumaysah, is illuminating (Via Tom Gara and Charles Lister):
It’s a scary portrait of a person of conviction, sober and in their right mind, who openly pines for the day when the U.K., too, is a Sharia state and refuses to renounce terror in order to achieve that objective. The report ends with the terrifying fact that at least 500 British citizens are currently fighting and training in the Islamic state.