Brussels was struck on Tuesday by major, apparently coordinated terrorist bombings, at the airport and on the metro system, that killed at least 31 people and injured hundreds. The attacks at the heart of the de facto capital of the European Union occurred only four days after the arrest in the city of Salah Abdeslam, Europe’s “most wanted man” and one of the Belgians linked to the Paris atrocities in November. He was caught after an intense police shoot-out, and Belgian authorities had previously warned of potential reprisals. Brussels terror attacks: ISIS jihadists strike heart of a fraying Europe The self-ascribed Islamic State (IS) terrorist group has claimed responsibility for the attacks. In subsequent raids in Brussels, authorities have discovered an IS flag and also a stack of chemical products, plus explosive devices containing nails. While key uncertainties remain, Belgian Foreign Minister Didier Reynders said at the weekend that Abdeslam “was ready to restart something in Brussels, and it may be the reality because we have found a lot of weapons, heavy weapons … and a new network around him in Brussels”. Key questions will now be asked about the preparedness of Belgian and wider European intelligence agencies for such attacks. Paris terrorist attacks underline the need to root out the causes that radicalise youth The fact that the atrocities were carried out by IS will fuel concerns about European citizens radicalised and drawn to the group by its propaganda. Some of these foreign jihadists have now returned to their home countries in Europe from the Middle East. The International Centre for the Study of Radicalisation in London estimates that as many as 11,000 foreigners may have fought in Syria alone, from some 74 countries, the majority from Arab countries. A central concern is that these individuals, who potentially include up to 2,000 from Western Europe, plus others from North America, Australia, Southeast Asia, and Africa, will return battle-hardened, with significantly greater terrorist capability and resolve. And it is believed that, per capita, Belgium is Europe’s biggest contributor of fighters to Syria, with Brussels a particular hot spot. US President Barack Obama has already expressed “deep concern” about this issue, echoing comments of others, including British Prime Minister David Cameron. Moreover, FBI director James Comey has even warned about the prospect of a “future 9/11” caused by the increased flow of these foreign fighters. Islamic State planning large-scale attacks in Europe What this underlines is that while Belgium was targeted on Tuesday, cities across the continent are potentially vulnerable, as the Paris attacks showed. This has been recognised by leaders including French President Francois Hollande, who noted that Tuesday’s attacks struck at “the whole of Europe”. The fact that this is a European-wide issue is reflected in the tightening of security across key sites on the continent. French Interior Minister Bernard Cazeneuve announced he was deploying 1,600 additional police to border crossings and air, sea and rail infrastructure. Meanwhile, it emerged earlier this month, only days before these latest attacks, that London’s police and security forces are working on the possibility that the capital could be hit by up to 10 attacks on the same day. What this reinforces is the fact that IS planning appears to be increasingly centred around multiple, sequenced atrocities, as Brussels underlines. 22,000 Islamic State jihadists have been killed by coalition, France claims This will provide an unfortunate propaganda coup for IS at a time when its fortunes in Iraq and Syria may be ebbing, with some reports that it may have lost around a fifth of the territory under its control in those two countries over the past 14 months, and potentially 40 per cent of its revenue, much of it from oil, according to research company IHS. In that sense, Tuesday’s terrible actions are a way for the network to try to re-emphasise to the international public its continued destructive capability in Europe, despite recent setbacks in the Middle East. Andrew Hammond is an associate at LSE IDEAS (the Centre for International Affairs, Diplomacy and Strategy) at the London School of Economics