How the U.S. Can Finish Off al-Qaeda

Lessons from a study of 300 terrorist leaders who were killed

Killing bin Laden will not be enough on its own. But by continuing to embrace the Arab spring and beginning massive withdrawals from Iraq and Afghanistan, the U.S. can finally defeat his war of terror.

A 2008 anti-U.S. demonstration in Lahore, Pakistan. Mohsin Raza / Reuters

With the death of Osama bin Laden, many are asking: What does this mean for the war on terror? Is it possible for the United States and its allies to put the fear of terrorism behind us, or are we destined to see al-Qaeda reconstituted, with fresh waves of attacks into the foreseeable future?

Bin Laden's death may well be the most important single step in the war on terror since 2001, but it creates an even larger opportunity for America and its allies. To capitalize on those gains and further undercut al-Qaeda's popular support, the U.S. may find that the best way forward in its war against al-Qaeda could be by withdrawing ground troops from its two other wars, partially from Afghanistan and completely from Iraq.

Over the past decade, we have studied every major terrorist attack since September 11, 2001, including all suicide attacks around the world (over 2,200 cases) and every instance of leadership "decapitation" -- in which the leadership of a terrorist group is killed -- (over 300 cases) in recent decades. As part of this work, we have studied al-Qaeda and its followers extensively.

Our research suggests that the death of Osama bin Laden could well become a major turning point in the war on terror, making Americans substantially safer -- but only if we follow up in the right way over the next year. If we do, and if we are very lucky, the war on terror could one day truly become a thing of the past.

Leadership decapitation on its own rarely lowers either the life expectancy of terrorist groups or their ability to carry out violent attacks, and our work shows it may sometimes have the opposite effect. Israeli forces assassinated numerous leaders of Hezbollah and Hamas with little success in reducing violence. In 2006, the U.S. killed Abu Musab Al-Zarqawi, the infamous terrorist leader in Iraq, only to see violence rise more than 50 percent the following year.

Particularly ominous are the findings on leadership decapitation for religious terrorist groups like al-Qaeda. The odds that a religious terrorist group will collapse in the wake of a decapitation are 17 percent. That is especially discouraging considering that the odds of such a group dissolving when there is no decapitation are 33 percent. Put differently, killing leaders of a religious terrorist group appears to increase the group's chances of survival from 67 to 83 percent.

What appears to matter most for the long-run trajectory of decapitated terrorist groups is popular support. The most successful groups are those with support that transcends the leader's charisma; their strength comes from promoting a popular agenda. The more popular the group's cause, the more resources and prestige it has to draw new leaders to replace those who are removed. Ten years of operation appears to be the crucial threshold -- the point after which groups with popular support can replace the loss of the top leader, often with younger individuals seeking to make a name for themselves through more aggressive attacks, and safely survive.

Terrorist groups like al-Qaeda that carry out campaigns of suicide attacks depend on significant popular support. Otherwise they would not be able to generate wave after wave of suicide missions that can cost the lives of their most ardent followers. Studies at the University of Chicago show that suicide bombing campaigns virtually always arise from popular resentment toward military occupation or territorial domination.

Al-Qaeda fits this pattern. For nearly two decades, the presence of large-scale U.S. ground forces in Muslim countries has been far and away al-Qaeda's principle recruiting asset. What made bin Laden famous in the first place was not his religious commitment to Islamic fundamentalism, which would hardly separate him from many other would-be Muslim leaders. Rather, bin Laden's popular support originally stemmed from his stance against U.S. ground forces in the Arabian Peninsula in the early 1990s.

Starting in the mid-1990s, bin Laden began giving sermons and long public pronouncements with titles like, "Declaration of War against the Americans Occupying the Land of the Two Holy Places." While many Americans focused on the references to Islam, what mainly drove bin Laden and his followers was what he called America's "veiled colonialism." The massive invasions in Iraq and Afghanistan have given al-Qaeda vastly more ideological material with which to recruit.

Two of the four London subway bombers -- all al-Qaeda followers -- left videos in 2007 attesting to this territorial motive. Suicide bomber Shehzad Tanweer said in his video that such attacks would "intensify and continue until you pull all of your troops out of Afghanistan and Iraq." Such suicide notes should not dictate American policy, but they offer insights into the persistent grievances that drive al-Qaeda's suicide bombers.

Another sign of those motives can be found in al-Qaeda's recruitment patterns. Of the 81 al-Qaeda suicide attackers whose identities we know, 70 came either from Sunni Muslim countries with heavy U.S. combat operations or from North African countries that had what al-Qaeda identified as U.S.-backed repressive regimes.

If we want to remove the popular support that allows al-Qaeda to survive, the best way is to make fundamental changes in U.S. foreign and military policies toward major Muslim countries. Since January, the Obama administration has already begin a dramatic shift away from shoring up authoritarian regimes in North Africa (and, to a lesser degree, the Middle East), which should make a major dent in al-Qaeda's recruitment from this area over time.

To the extent that we can further roll back al-Qaeda by force, it will be mostly through additional intelligence operations and covert activities like the raid that killed bin Laden, not large-scale military action. Operations like these allow us laser-like focus on a particular objective and increase the chances of success. Large-scale military operations not only take our focus off of the main objectives, but they can create many other problems: namely, fueling the popular support of groups like al-Qaeda and creating an environment that will allow future bin Ladens to gain strength.

To strike an even more devastating next blow against al-Qaeda's recruitment, President Obama should begin major military withdrawals now while the group is reeling from the changes in the Arab world and from the loss of bin Laden. By completing the U.S. withdrawal from Iraq and removing significant forces from Afghanistan starting in July, as Obama initially pledged to do in his December 2009 speech on the war there, the U.S. can truly cut the fuse of the threat to America and to Americans.