I'll open my first contribution with a confession: I chose a deliberately provocative title. Though of course I did this to draw attention, the statement is nevertheless true.
Before delving into why, let's ask an easier question: Why is the title provocative? In other words, why would we expect military force to work in counterterrorism and counterinsurgency? The reason, I believe, is that in both terrorism and insurgency there are armed, organized people trying to kill us. This recalls war, and anything short of a show of military force in war smacks of appeasement. Even if a settlement is sought, force acts as a signal of strength. And without force, an enemy comparable to us in strength can run right over us.
Instead, what terrorist and insurgent groups do is act to influence important audiences into siding with their positions. There are many examples of this. When groups rely on a steady drumbeat of casualties, they hope that this strategy of attrition will convince civilian or military leaders to pressure the government to capitulate to avoid further losses. When extremist groups attack to spoil peace processes between government and more moderate groups, they hope to convince elites that there is no sense negotiating since it won't stop the attacks and the moderate group may not be trustworthy. And when groups attempt to provoke governments to use significant military force that causes damage, injury and death to non-combatants, they hope to convince the surrounding population (and potentially other nations) that their cause is just and their opponent horrible.
What all these strategies have in common is that they rely upon the perception of others. If the group's audience is not influenced, the group is ineffective. In light of this, consider two strategies, one based on military force and the elimination of the enemy (drone strikes, special forces, etc.) and the other based on garnering the support of the surrounding population. The latter is typically called "hearts and minds."
Military force is generally effective at causing a direct reduction in the capability of the group. This direct effect also leads to an indirect reduction in the surrounding population's support for the group; reducing examples of the group's strength diminishes others' incentives to support it. However, unless force eliminates globally visible elements of the group such as Osama bin Laden, this indirect effect is largely confined to audiences familiar with the elements of the group eliminated. For example, the targeted killing of a group commander with few ties to the local community would likely have little effect on the community's level of support for the group. Further, force can trigger backlash. The net effect of all this tends to be that force decreases support for a group locally, but increases it further away from the target of the force.
Hearts and minds, in contrast, has two global effects. First, there's a direct global reduction in support for the group as the grievances which helped make the group attractive in the first place are diminished by improving infrastructure, security, education and so on. Second, because this effect is global, it's observed by everyone, and so the indirect effect of observing others' decrease of support is also global. The net effect is a decrease in support for the group locally and globally.
When one compares these two approaches to counterinsurgency and counterterrorism, one finds that comparable levels of hearts and minds are generally superior to military force even without backlash, and trump force with backlash. See here for more on this. There are two exceptions. One, force can be more effective than a hearts-and-minds approach when it can be applied overwhelmingly. Two, force can be very effective if the group has very localized support that has not spread and the source of its support is isolated from the rest of the population. These two cases provide a pretty narrow window for the use of force, particularly in regions in which collateral damage and injury are virtually impossible to avoid completely, despite extensive and noble efforts to do so.
This takes us back to the title: Military force is usually the wrong choice for counterterrorism and counterinsurgency. If you still don't like that, compare it to disease. Quarantine acts very similarly to military force, removing diseased individuals from the population, while vaccines are like hearts and minds, imperfectly reducing individuals' susceptibility to disease. We decided long ago what our national strategy should be there.
Siegel is an associate professor of political science at Duke University.