Mostly Quiet on the Western Front

While the horrific bombing at the Boston Marathon has brought concerns about terrorism back to the forefront of national attention, it is worth remembering that terrorism inside the United States is exceedingly rare. Over the past 40 years, just over 3 people on average have been killed by acts of terrorism per year (remove 9/11, and the average is 1.4 deaths per year).

To put this in some context, over 122,000 Americans died from accidental injury in 2011, while 53,000 died from the flu and pneumonia. Terrorism is also rarer now than in past decades -- there were 1,357 terrorist attacks in the United States in the 1970s, but only 168 in the 10 years after 9/11.

Our instincts tell us that terrorism ought to be quite common. In our open, modernized society where dangerous technology is cheap and prevalent, it is not difficult to figure out how to cause massive harm. Instructions on making pipe bombs or other incendiary devices are only a Google search away. Equipment to make bombs, like the ones detonated in Boston, requires not much more than a trip to RadioShack and a hardware store. There is also no shortage of targets. Large numbers of people are frequently gathering together in places that have little or no security presence, whether at high school football games, bus stations, or dance recitals. After 9/11 or an event like the Boston attack, we often think "it would be so easy to [fill in the blank] and cause massive damage." And it's true.

Then why doesn't it happen more often?

The main reason is that there just aren't that many would-be terrorists in the United States. Even though we live in a violent society where about 15,000 murders occur every year, terrorism is a specialized form of violence that is attractive to only a very few people. Most violent crime results from domestic confrontations, the illegal drug trade, and ordinary street-level disputes. Terrorism, however, is the use of violence to advance a political purpose. Terrorists generally have deep grievances about the state of the world and want to draw attention to their causes through the most dramatic fashion possible -- the use of violence to cause death and destruction.

But the process of moving from a law-abiding citizen to violent killer in the name of politics is not an easy path to follow. Many things can divert the would-be terrorist along the way: interest in the cause can wane, a family member might need help, the prospect of martyrdom loses its glamour and appeal, or any number of other factors. People who begin down the radicalization process often disengage from the terrorist enterprise or lose their ideological zeal. Very few individuals with extremist views ultimately undergo the psychological transformation that brings them to the point of causing violence against innocents. Moreover, the number of Americans who have such deep-seated political grievances that they are motivated to commit violence just to make a point is tiny.

In fact, many Americans couldn't care less about politics. Those who do generally accept the normal rule that disagreements are decided through elections or legislation. Sure, there is vitriol in American politics. But free speech and debate serves as a release valve for pent-up ideological animosities. Terrorists are the rare birds who become psychologically attached to a political cause and reject normal politics as a means for addressing their grievances.

While no domestic controversies have resulted in serious enough grievances to sustain significant amounts of terrorism over the past 50 years, the al Qaeda movement that emerged in the 1990s did generate significant numbers of terrorists abroad hostile to the United States. They were motivated by a perception that U.S. foreign policy and other assertions of power have had a derogatory impact on Islam and those who practice it around the world. The 9/11 attacks were such a shock, in part, because Americans did not understand the depth of this movement or their vulnerability to an enemy willing, even eager, to die for a cause.

Despite the controversies surrounding some elements of the response to 9/11, by and large, it has been remarkably effective in preventing al Qaeda-inspired terrorism inside the United States. Since 9/11, there have been no successful attacks inside U.S. borders planned and executed by foreign nationals emanating from abroad -- and only 10 successful homegrown attacks, which have caused just 17 deaths. This is a record most would have thought impossible in the nervous days and months after September 2001.

The key elements of this counterterrorism strategy have been the application of military force by the United States and its partners in strategic areas around the world, a globally coordinated intelligence collection effort, a large scale shift of federal law enforcement resources to preventing terrorism, a much more rigorous vetting of visa applicants from high-risk countries, and greater border security and immigration controls.

The use of force abroad has reduced the supply of active terrorists by killing many senior al Qaeda members and dampening the allure of al Qaeda to potential recruits. The adventure of training in the Hindu Kush and fighting against foreign infidels once had a romantic allure to many -- hiding from American drones in the hinterlands of Pakistan does not.

We have also benefitted from a strategically inept enemy. Al Qaeda's intolerance and brutality has managed to alienate local populations wherever they have gained a foothold. Al Qaeda in the Islamic Maghreb is so despised by most Malians that they cheered the tanks of their former colonial oppressors as they rolled through Timbuktu to chase out the extremists. It is true that al Qaeda has formed affiliate groups that have spread to Africa, the Middle East, and South Asia, but it appears recently that most of them are more focused on addressing regional grievances than attacking the United States proper. Notice how quickly the Pakistani Taliban disavowed any connection to the attacks in Boston.

Tightened immigration controls have undoubtedly made it more difficult for foreign terrorists to get to the United States. We know this is true because al Qaeda shifted its strategy from attempting to sneak trained foreign operatives into the United States to recruiting individuals who already live within the country to launch homegrown attacks. While this strategy showed some early initial success with the Fort Hood shooting and attempted explosives attacks on New York by Najibullah Zazi and Faisal Shahzad, it has fizzled of late. In 2009, 50 Muslim Americans were arrested for participating in a terrorist plots; by 2012, that number had dropped to 14 -- and only two Muslim Americans have been arrested on terrorism charges so far in 2013.   

Terrorism also continues to be rare in the United States because the substantial resources committed to law enforcement agencies have enabled them to preempt most of the terrorist plots initiated since 9/11 prior to any violence occurring. These successful prosecutions appear to have resulted from the use of tried and true investigative tactics and techniques -- with hints and clues coming from the community and informants leading to warrants for electronic surveillance that ultimately produce evidence to support an arrest. Potential terrorists also leave many clues in chat rooms and social media sites. The public perception is that terrorists are criminal masterminds, but most are not: many of them like to boast of their grand ideas and plans for violence to others, either in person or on the Internet. But once they do, they usually come to the attention of the police and ultimately find themselves behind bars.

And yet, the fact that terrorism is rare is little solace to the victims of the brutal attack that killed three young people and caused so many devastating injuries in Boston. This attack was a sobering reminder that terrorism is not going to disappear anytime soon. But it would be a mistake to assume that a new wave of terrorism has begun. Americans are more likely to be struck by lightning than killed in a terrorist attack. We have to keep this in mind in determining how our society and our government should respond to the attack on the Boston Marathon.

David H. Schanzer is associate professor of the practice of public policy and the director of the Triangle Center on Terrorism and Homeland Security at Duke University, the University of North Carolina Chapel Hill, and RTI International. This commentary was originally published in Foreign Policy magazine.