The death of Osama bin Laden on Sunday, after more than a decade of pursuit, is a huge symbolic victory for U.S. forces. If the history of counterterrorism is any guide, the action will also inspire a desire for retribution among al Qaeda and its myriad affiliate groups throughout the world. The threat is real but not as great as it might loom in our imaginations, argues sociologist Charles Kurzman at the University of North Carolina at Chapel Hill. Kurzman is an expert on the Middle East and social movements. He is author of The Missing Martyrs: Why There Are So Few Muslim Terrorists, forthcoming from Oxford University Press in the summer. Scientific American asked him to weigh in on the terrorist threat we might anticipate in the wake of Bin Laden's death.

What do you make of bin Laden's death?
It shows the extent to which al Qaeda has shrunk in the past 10 years. If you compare the size of the training camps that al Qaeda had during Taliban era, when they trained thousands of militants [in Afghanistan], since then the camps have been much smaller in size. Now there are generally no more than a couple dozen trainees at a time, because satellite surveillance and other intelligence sources are constantly watching, and any larger groups would attract attention.

What is the threat from al Qaeda or groups affiliated with it, who may want to retaliate for bin Laden's death?
There's consistently been retribution toward each of our major counterterrorism offenses. And vice versa—each act of terrorism generates retribution from the U.S. The capability of terrorists to attack has not changed. Their desire has not changed. The death of this single individual is symbolically important, but probably not significant operationally. This does not change the overall threat profile, which was low two days ago, and is low today.

Why so?
Al Qaeda Central has not been too active in recent years. It's been chased to the ends of the world, and it really is not the center of action for global terrorism any more. That center has shifted to local affiliate groups in Yemen, Pakistan, Southeast Asia, Northwest Africa, which are only loosely linked to the center. They don't rely on the center for funding and training. Fortunately for the world, they are less competent, less well-trained. They manage to kill people each year, but not too many.

What do the data show?
There are two sources of global data. The Global Terrorism Database at the University of Maryland lists data since 1970 of more than 80,000 terrorist incidents. The number of fatalities from terrorism peaked at 12,000 per year in 2007, and it's now down to under 10,000. That's similar in scale to peaks in the 1980s and 1990s. If we take out Pakistan, Afghanistan and Iraq, the number of fatalities is under 5,000, which is one of the lowest figures since 1980.

The other database is kept by the White House's National Counterterrorism Center. It shows a peak of 22,000 fatalities in 2007, which went down to 10,000 in 2010. Again, that goes to 5,000 if take out those three countries. Most of the incidents at the peak [occurred] in Iraq.

There have been reports, though, that activity in the U.S. among local groups is on the rise.
In our updated report from February [pdf], incidents dropped by more than half so far in 2011. We got attention to this downturn because [Representative] Peter King was asked about this report in Congressional hearings, and said our report was biased.

What about the report last year by Peter Bergen and Bruce Hoffman, who say that the threat from al Qaeda affiliate groups is "more complex and more diverse than at any time over the past nine years"? 

The problem with that report is they include terrorism financing cases in the last year. Convictions for terrorism financing skew the trend line upwards. To count [financial terrorism cases going back a decade or so] would be a challenge, because a lot of [the data] would be ambiguous. That's why we decided in our report just to include violent events.

What are the policy conclusions to draw from the low numbers you cite?
I would like to see the public debate about each of the nation's security measures be reasonable and based on evidence. Let's turn down the volume of fear and paranoia and have a reasonable discussion about the costs and benefit of these security measures, given what we know about the level of threat. As we approach the anniversary of 9/11, we should be relieved to see that the feared explosion in terrorism has not occurred.