The ending of most terrorist groups requires a range of policy instruments, such as careful police and intelligence work, military force, political negotiations, and economic sanctions. Yet policy makers need to understand where to prioritize their efforts with limited resources and attention. Following an examination of 648 terrorist groups that existed between 1968 and 2006, we found that a transition to the political process is the most common way in which terrorist groups ended (43 percent). The possibility of a political solution is inversely linked to the breadth of terrorist goals. Most terrorist groups that end because of politics seek narrow policy goals. The narrower the goals of a terrorist organization, the more likely it can achieve them without violent action—and the more likely the government and terrorist group may be able to reach a negotiated settlement.
Against terrorist groups that cannot or will not make a transition to nonviolence, policing is likely to be the most effective strategy (40 percent). Police and intelligence services have better training and information to penetrate and disrupt terrorist organizations than do such institutions as the military. They are the primary arm of the government focused on internal security matters. Local police and intelligence agencies usually have a permanent presence in cities, towns, and villages; a better understanding of the threat environment in these areas; and better human intelligence.
Other reasons are less common. For example, in 10 percent of the cases, terrorist groups ended because their goals were achieved, and military force led to the end of terrorist groups in 7 percent of the cases. Militaries tended to be most effective when used against terrorist groups engaged in an insurgency in which the groups were large, well armed, and well organized. Insurgent groups have been among the most capable and lethal terrorist groups, and military force has usually been a necessary component in such cases. Against most terrorist groups, however, military force is usually too blunt an instrument. Military tools have increased in precision and lethality, especially with the growing use of precision standoff weapons and imagery to monitor terrorist movement. But even precision weapons have been of limited use against terrorist groups. The use of substantial U.S. military power against terrorist groups also runs a significant risk of turning the local population against the government by killing civilians.
Our quantitative analysis looked at groups that have ended since 1968 or are still active. It yielded several other interesting findings:
- Religious terrorist groups take longer to eliminate than other groups. Approximately 62 percent of all terrorist groups have ended since 1968, but only 32 percent of religious terrorist groups have ended.
- Religious groups rarely achieve their objectives. No religious group that has ended achieved victory since 1968.
- Size is a significant determinant of a group’s fate. Big groups of more than 10,000 members have been victorious more than 25 percent of the time, while victory is rare when groups are smaller than 1,000 members.
- There is no statistical correlation between the duration of a terrorist group and ideological motivation, economic conditions,regime type, or the breadth of terrorist goals. But there appears to be some correlation between the size of a terrorist group and duration: Larger groups tend to last longer than smaller groups.
- When a terrorist group becomes involved in an insurgency, it does not end easily. Nearly 50 percent of the time, groups ended by negotiating a settlement with the government; 25 percent of the time, they achieved victory; and 19 percent of the time, military forces defeated them.
- Terrorist groups from upper-income countries are much more likely to be left-wing or nationalist and much less likely to be motivated by religion.