The anti-ISIS coalition has clearly been less successful in two other dimensions of the strategy: putting intelligence and surveillance barriers between ISIS’s territorial holdings and civilian targets abroad, and undercutting ISIS's ideological appeal. These are harder problems than military containment. The free movement of people and information is a defining feature of globalization. It does not take many people to conduct an attack of the kind that occurred in Paris. Those people do have to be highly motivated, however, and reducing the political commitment that comes from the spread of very poisonous ideas to small numbers of young men is a hard problem.
The United States has been quite energetic on the intelligence and surveillance front, but others closer to the fight have not done enough. Coverage of the Charlie Hebdo attacks in January 2015 revealed that the French security services simply had inadequate resources to track possible threats. This kind of shortfall probably exists across much of Europe. Moreover, the problem confronted by European security and intelligence organizations is greater than that confronted by the United States. European countries are closer to the Middle East; it is simply easier for ISIS terrorists to get there. There are large, sometimes poorly integrated Arab communities in Europe that, through no fault of their own, can provide a kind of camouflage for small numbers of conspirators. Sadly, some disgruntled members of these communities are susceptible to radical appeals, and sign up or offer succor.
Finally, Europe suffers from a simple tension: Europeans have organized their social and economic life as if the European Union were one country, but European states’ political and security life is organized as if each was still a separate, sovereign country. Terrorists (and criminals) can wander at will across a vast expanse of land and people; as they do so they move from the purview of one national-security organization to the next. European security organizations do cooperate, but there will inevitably be gaps that clever bad guys can exploit. There is no obvious answer to these three problems. That said, more resources would help, and the Europeans must invest more in the internal security aspect of the fight. And, unfortunately, the European Union may have to take a step backwards on social and economic integration, and a step forward on security integration, working more strenuously for cooperation among national police and intelligence organizations.
Turkey poses a delicate political-military problem in the fight against ISIS. It has been a consistent refrain that Turkey has not done everything that it could to monitor, much less control the transit of, volunteers to and from the Syrian Civil War—many of whom are Europeans of Arab descent. These volunteers are traveling to join any one of the many groups fighting the Assad regime, some of which Turkey supports. But, judging from published figures, thousands have joined ISIS, and some of them have subsequently returned to their home countries, trained and ready to participate in terrorist actions. The U.S. air effort against ISIS has profited from the recent opening of Turkish air bases, which facilitate strikes against the group’s holdings in northeastern Syria. So it is a delicate diplomatic matter to criticize Turkish surveillance policy. Nevertheless, without more Turkish cooperation to control the transit of potential terrorists, Western Europe will remain vulnerable, and ISIS will replenish its ranks with foreign volunteers. This issue must be confronted forthrightly.