Over 15,000 foreign jihadists from 80 countries are believed to be fighting alongside militants in Syria, the CIA says. The Syrian war is estimated to have mobilised more European Islamists than all the foreign wars of the last 20 years combined. What to do when the jihadists try to return home? Many of them might be trained to wage jihad against their home countries. The danger is, as Daniel Byman and Jeremy Shapiro write in the current issue of Foreign Affairs, “The returned fighter seasoned by battle acquires a new authority among his old friends and followers on social media – a street cred that allows him to recruit and radicalise others and send them into the fray.” On the other hand, because of the use of social media where the returnee sometimes brags about his exploits and adventures, it becomes easy for intelligence services both to track him down and know who he is trying to reach.The threat posed by returning jihadists is too often hyped by both western politicians and the media. The numbers that go to fight from western countries is only about 2,500. Of course, even if only 25 percent at some point return that could be enough to cause mayhem, if that is what they are intent on doing. The impression that one used to get is that, until a few months ago, the jihadists did not think that much about their home countries. They were driven not by the wrongs at home but by the clarion call of the ultra militants of their Muslim sect, the Sunni, who want to cut down the Shias and establish their own caliphate. But now western airstrikes on the Sunni fighters of the Islamic State (IS) by western and Arab Gulf nations are well established – they began in August – there is talk among the foreign fighters about bringing home the war in revenge.Even so, the situation must be kept in proportion. It used to be said there would be “blowback” from the war in Iraq. It did not happen. Second, many of these volunteers will never return as they will die in combat – the ferocity of the present fighting exceeds that of other recent conflicts – or join new military campaigns elsewhere or return home disillusioned and peacefully inclined. Third, thanks to pervasive intelligence, they are often arrested on their return. This year alone, the UK police say they have arrested 218 returnees and 40 British citizens are awaiting trial on terrorism charges. In Europe, five terrorist plots have been foiled but there has been no serious successful terrorism on European or US soil for a number of years. Fourth, the number of returnees who are still militants is not particularly large. One study found that only one in nine western fighters who went abroad between 1990 and 2010 came back determined to attack home targets.Iraq offers other lessons. During the war against Iraq, initiated by President George W Bush and UK Prime Minister Tony Blair, dozens of Muslims from the US and Europe went to fight. Many became even more radicalised during the fighting and joined al Qaeda after it established a local affiliate in 2004. In 2005, the director of the CIA, Porter Goss, warned the Senate Select Committee, “Islamist extremists are exploiting the Iraqi conflict to recruit new anti-US jihadists.” In fact, terrorists failed to perpetuate attacks in the west, apart from a bungled one at Glasgow airport in 2007 (this was carried out not by returning jihadists but by a tiny group of home-grown al Qaeda sympathisers.) The experience of Iraq also points towards another problem for jihadism: infighting among militants. The IS jihadists have to look three ways: towards the governments of Syria and Iraq, towards the danger from the sky and the threat from the less extreme militants in Syria who, although fighting the regime of President Bashar al-Assad, want to see IS eradicated.But what to do about those who do try and return home to wage war? The UK government already has a policy in place that allows it to seize the passports of those it suspects of terrorism. That is one way to go. Another, as practiced in Saudi Arabia and Denmark, is to develop policies that would reintegrate them back into normal society. In Aarhus, Denmark, returning jihadists are met with counselling and career advice rather than jail. The thinking behind the Aarhus model is straightforward. Many of those who left were young men, some with few prospects, who did not feel welcome in Danish society. Interrogating and arresting them on their arrival could further radicalise them, but engaging them in dialogue might not.In Saudi Arabia there are special (comfortable) detention facilities where returnees can learn true Islamic teaching, get counselling from psychologists and get job training. It does not always bear fruit but often enough it does. There is no real workable alternative. The writer has been a foreign affairs columnist for the International Herald Tribune for 20 years and author of the much acclaimed new book, Conundrums of Humanity – the Big Foreign Policy Questions of Our Age. He may be contacted at jonathanpower95@gmail.com