More systematically, the economists Jason Lindo and María Padilla-Romo examined the effects of targeting high-ranking gang members on Mexican homicide rates from 2001 to 2010. This “kingpin strategy,” they found, increased homicides by 80 percent in the municipalities where the leaders had operated for at least one year.
Many militant groups have also become less restrained toward civilians after the death or imprisonment of senior figures. In 1954, the British launched Operation Anvil to stamp out the Mau Mau Uprising in Kenya. Capturing leaders around Nairobi initiated a period of uncoordinated, rudderless violence. South Africa’s African National Congress also became less tactically disciplined when its leadership was marginalized. In 1961, the ANC established an armed wing called Umkhonto we Sizwe, which came to be known as the MK. Leadership stressed the value of “properly controlled violence” to spare civilians. For three years, MK members complied by studiously avoiding terrorist attacks. After Nelson Mandela was sentenced to life imprisonment in 1964, however, young men in the ANC engaged in stone throwing, arson, looting, and brutal killings of civilians. The political scientist Gregory Houston observed that “the removal of experienced and respected leaders … created a leadership vacuum” that empowered undisciplined hotheads. When Filipino police assassinated the Abu Sayyaf founder, Abdurajak Abubakar Janjalani, in 1998, the group devolved into a movement of bandits that preyed on private citizens. When Nigerian police summarily executed the Boko Haram founder, Mohammed Yusuf, in 2009, the terrorist organization also turned ruthless against civilians. And the al-Qaeda–linked rebel group Ahrar al-Sham became even more radical after a 2014 attack on its headquarters, in the northwestern province of Idlib, Syria, took out its leadership.
The theory that removing leaders results in worse violence is supported by more than mere anecdote. In a couple of peer-reviewed studies, I’ve tested whether killing the leader of a militant group makes that group more tactically extreme. Across conflict zones from the Afghanistan-Pakistan to the Israel-Palestine theaters, my co-authors and I found that militant groups significantly increase their attacks against civilians after an operationally successful strike against their leadership. Vengeance is not the main driver, as the overall quantity of violence changes less than the quality does. So-called leadership decapitation does not elicit a paroxysm of violence, but makes it more indiscriminate against innocent civilians.
Leadership decapitation promotes terrorism by empowering subordinates with less restraint toward civilians. In empirical research, I’ve demonstrated that militant groups fare better politically when they direct their violence at military and other government targets rather than civilians. Unlike guerrilla attacks against government targets, terrorist attacks against civilian targets tend to reduce popular support, empower hard-liners, and, most important, lower the odds of government concessions. But lower-level members, compared with their superiors, are less likely to grasp that attacking civilians does not pay.