Game theorists posit that even suicide bombers are rational actors. Illustration by Francesco Bongiorni

A few days after the September 11th attacks—which killed seven times as many people as any previous act of terrorism—President George W. Bush declared that the United States was engaged in a global war on terror. September 11th seemed to confirm that we were in a clash of civilizations between modernity and radical Islam. We had a worldwide enemy with a cause that was general, not specific (“They hate our freedoms”), and we now had to take on the vast, long-running mission—equal in scope to the Cold War—of defeating all ambitious terrorist groups everywhere, along with the states that harbored them. The war on terror wasn’t a hollow rhetorical trope. It led to the American conquest and occupation first of Afghanistan, which had sheltered the leaders of Al Qaeda, and then of Iraq, which had no direct connection to September 11th.

Today, few consider the global war on terror to have been a success, either as a conceptual framing device or as an operation. President Obama has pointedly avoided stringing those fateful words together in public. His foreign-policy speech in Cairo, last June, makes an apt bookend with Bush’s war-on-terror speech in Washington, on September 20, 2001. Obama not only didn’t talk about a war; he carefully avoided using the word “terrorism,” preferring “violent extremism.”

But if “global war” isn’t the right approach to terror what is? Experts on terrorism have produced shelves’ worth of new works on this question. For outsiders, reading this material can be a jarring experience. In the world of terrorism studies, the rhetoric of righteousness gives way to equilibrium equations. Nobody is good and nobody is evil. Terrorists, even suicide bombers, are not psychotics or fanatics; they’re rational actors—that is, what they do is explicable in terms of their beliefs and desires—who respond to the set of incentives that they find before them. The tools of analysis are realism, rational choice, game theory, decision theory: clinical and bloodless modes of thinking.

That approach, along with these scholars’ long immersion in the subject, can produce some surprising observations. In “A Question of Command: Counterinsurgency from the Civil War to Iraq” (Yale; $30), Mark Moyar, who holds the Kim T. Adamson Chair of Insurgency and Terrorism at the Marine Corps University, tells us that, in Afghanistan, the Taliban’s pay scale (financed by the protection payments demanded from opium farmers) is calibrated to be a generous multiple of the pay received by military and police personnel (financed by U.S. aid); no wonder official Afghan forces are no match for the insurgents. Audrey Kurth Cronin, a professor of strategy at the National War College, reminds us, in “How Terrorism Ends: Understanding the Decline and Demise of Terrorist Campaigns” (Princeton; $29.95), that one can find out about Al Qaeda’s policy for coördinating attacks by reading a book called “The Management of Barbarism,” by Abu Bakr Naji, which has been available via Al Qaeda’s online library. (Naji advises that, if jihadis are arrested in one country after an attack, a cell elsewhere should launch an attack as a display of resilience.) In “Radical, Religious, and Violent: The New Economics of Terrorism” (M.I.T.; $24.95), Eli Berman traces the origins of the Taliban to a phenomenon that long preceded the birth of modern radical Islam: they are a direct descendant of the Deobandi movement, which began in nineteenth-century India in opposition to British colonial rule and, among other things, established a system of religious schools.

What is terrorism, anyway? The expert consensus converges on a few key traits. Terrorists have political or ideological objectives (the purpose can’t be mere profiteering). They are “non-state actors,” not part of conventional governments. Their intention is to intimidate an audience larger than their immediate victims, in the hope of generating widespread panic and, often, a response from the enemy so brutal that it ends up backfiring by creating sympathy for the terrorists’ cause. Their targets are often ordinary civilians, and, even when terrorists are trying to kill soldiers, their attacks often don’t take place on the field of battle. The modern age of suicide terrorism can be said to have begun with Hezbollah’s attack, in October of 1983, on U.S. marines who were sleeping in their barracks in Beirut.

Once you take terrorists to be rational actors, you need a theory about their rationale. Robert Pape, a political scientist at the University of Chicago, built a database of three hundred and fifteen suicide attacks between 1980 and 2003, and drew a resoundingly clear conclusion: “What nearly all suicide terrorist attacks have in common is a specific secular and strategic goal: to compel modern democracies to withdraw military forces from territory that the terrorists consider to be their homeland.” As he wrote in “Dying to Win: The Strategic Logic of Suicide Terrorism” (2005), what terrorists want is “to change policy,” often the policy of a faraway major power. Pape asserts that “offensive military action rarely works” against terrorism, so, in his view, the solution to the problem of terrorism couldn’t be simpler: withdraw. Pape’s “nationalist theory of suicide terrorism” applies not just to Hamas and Hezbollah but also to Al Qaeda; its real goal, he says, is the removal of the U.S. military from the Arabian Peninsula and other Muslim countries. Pape says that “American military policy in the Persian Gulf was most likely the pivotal factor leading to September 11”; the only effective way to prevent future Al Qaeda attacks would be for the United States to take all its forces out of the Middle East.

By contrast, Mark Moyar dismisses the idea that “people’s social, political, and economic grievances” are the main cause of popular insurgencies. He regards anti-insurgent campaigns as “a contest between elites.” Of the many historical examples he offers, the best known is L. Paul Bremer’s de-Baathification of Iraq, in the spring of 2003, in which the entire authority structure of Iraq was disbanded at a stroke, creating a leadership cadre for a terrorist campaign against the American occupiers. One of Moyar’s chapters is about the uncontrollably violent American South during Reconstruction—a subject that a number of authors have turned to during the war on terror—and it demonstrates better than his chapter on Iraq the power of his theory to offend contemporary civilian sensibilities. Rather than disempowering the former Confederates and empowering the freed slaves, Moyar says, the victorious Union should have maintained order by leaving the more coöperative elements of the slaveholding, seceding class in control. Effective counterinsurgency, he says, entails selecting the élites you can work with and co-opting them.

In “Talking to Terrorists: Why America Must Engage with Its Enemies” (Basic; $26.95), Mark Perry describes a little-known attempt to apply Moyar’s model in Iraq. The book jacket identifies Perry as “a military, intelligence, and foreign affairs analyst and writer,” but his writing conveys a strong impression that he has not spent his career merely watching the action from a safe seat in the bleachers. Much of the book is devoted to a detailed description, complete with many on-the-record quotes, of a series of meetings in Amman, Jordan, in 2004, between a group of Marine officers based in Anbar province, in western Iraq, and an Iraqi businessman named Talal al-Gaood. Gaood, a Sunni and a former member of Saddam Hussein’s Baath Party, suggested he could broker a deal that would make the horrific, almost daily terrorist attacks in western Iraq go away.