Estimates on the number of foreign jihadists in Syria and Iraq vary wildly. The CIA’s estimate is that there are 15,000 fighters from 80 different countries in Syria alone.
That’s a big problem for Syria right now, but it’s a big problem for 80 different countries in the future, if and when those fighters start to return home from their jihad.
Most Western nations with large jihadist populations are vowing detentions of returnees, and Britain has even threatened to revoke citizenship for those who stay in Syria for two years or more.
Making good on the threats, however, depend in large measure on those countries being able to identify the jihadist returnees, and intelligence on who those fighters are is nowhere near as good as officials sometimes claim.
Returnees from Syria who were visiting relatives or working for aid groups are liable to get swept up in the eagerness to capture jihadists, and may even be more vulnerable, since the jihadists tend to be much more covert about sneaking into Syria, and presumably will also be careful when sneaking back out.