Bessma Momani is an associate professor at the University of Waterloo and a senior fellow at the Centre of International Governance Innovation (CIGI); Lorne Dawson is an associate professor at the University of Waterloo.

Canada's involvement in the military campaign against Islamic State (IS) carries an added risk if we win: the return of foreign fighters to home soil. Canada's Bill C-51 is ill equipped for this unintended consequence and we need to prepare.

The academic literature on terrorism is largely informed by understanding and combating al-Qaeda, but IS poses new challenges. Al-Qaeda's strategy was to create as many world franchises of its terror model as possible, by supporting and financing cells to carry out attacks. It resembled a network of semi-autonomous nodes that adopted its perverse ideology.

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Battling al-Qaeda posed a challenge because defeating or suppressing a node did not root out the organization. Plenty of other nodes filled the ideological and political vacuum. This is why the military fight against al-Qaeda was often described as a whack-a-mole strategy. While there were self-proclaimed commanders and leaders headquartered in the Afghanistan-Pakistan area, analysts often noted how al-Qaeda did not have full control over its franchises; the self-declared independence of IS from al-Qaeda is testament to the stark limits of its control.

IS is an entirely different creature than al-Qaeda, and this may have an unintended consequence for Western governments fearful of a wave of foreign fighters going to fight with IS. Unlike al-Qaeda, IS operates with a much tighter and hierarchical command and control structure. IS has a charismatic leader at the helm that runs a tight ship. Holding on to a defined territory allows IS to play the role of a quasi-state, at least in a substantive, if not legitimate sense.

The military battle against IS continues to be ramped up with added muscle, training, and determination of both Western and Arab governments to attack IS's territorial holdings. But, herein lies the risk: if the coalition is successful in crippling IS, reversing its successes, and perhaps killing the top rung of IS commanders (especially the charismatic leader Abu Bakr al-Baghdadi), the leaderless foot soldiers will not have the directive or direction to continue, and they will begin to flood home. Or, if Mr. al-Baghdadi is simply backed into a corner, he will lash out with more direct attacks on the West to protect his diminishing charismatic authority.

With estimates on the IS force at 30,000 (numbers range from 10,000 to 50,000), the elimination of the top cadre means IS recruits will be without a rudder. That may seem like a good thing, but what we haven't given serious enough thought to dealing with the thousands of foreign fighters with Western passports, including the 40 or more Canadians who have left to join IS.

The provisions of Bill C-51 attempt to stem the supply side of terrorism, by censoring online conversations and beefing up CSIS and RCMP capacities. But the bill does not have a strategy to tackle the demand side of the problem, such as de-radicalization programs, building capacities and resilient communities through political empowerment, and supporting alternative narratives in vulnerable demographic groups. Security measures have a troubling tendency to feed back into the radicalization process itself. If IS is decapitated, the threat posed from returning fighters is theoretically higher than if it is simply contained, and it is unlike the consequences of defeating al-Qaeda for the radicalization of Western youth.

What can be done? Investing in prevention tools can help stop the feedback loop that could further radicalize new recruits and returning fighters. Prevention means we need to understand the appeal of IS as a cult, couched in medieval misinterpretations of an otherwise peaceful religion. Stemming the supply and re-offence of returnees requires detoxing wannabe fighters; understanding how vulnerable youth and misfits are searching for identity online; working with religious and community leaders to help would-be radicals discern the difference between scripture and propaganda; and de-glorifying the violence and militancy of travelling to Syria or other fronts. Disillusioned returnees can be used to describe the mundane and hypocritical life under IS rule. Some of the fighters who have returned to civilian life tell tales of how quickly they became disenchanted, as they were assigned to cleaning toilets and working Twitter accounts, and not trusted with combat or decision-making roles. This is not to say that we can expect a flood of 'innocent' returnees, but there will be some and we ought to be prepared with a variety of tools to suppress further radicalization other than our prison system.

Investing in de-radicalization/reintegration programs will address the demand side of terrorism that Bill C-51 does not. This will cost money and require considerable ingenuity, but other nations facing a much more severe threat from returnees, such as Germany and Denmark, have initiated such programs. The government should acknowledge that using the law may seem like a quick and cheap fix, but ignoring the need for a more "sociological" approach will cost more in the long run.