The Islamist terrorist group Boko Haram gained worldwide infamy in April 2014 when it kidnapped 276 girls from a boarding school in Chibok, Nigeria.

Now, thanks to two recent studies published by the Combating Terrorism Center at the U.S. Military Academy at West Point, New York, and authored by Elizabeth Pearson and Jason Warner and Hilary Matfess respectively, we know that the kidnapping raid was the beginning of an appalling evolution in Boko Haram’s use of women and girls in its terrorist activities.

Prior to 2014, Boko Haram used only male suicide bombers. Two months after the Chibok kidnappings, however, the group dispatched its first female suicide bomber, which proved to be the start of a terrible trend.

By the end of 2014, females had perpetrated the majority of all bombings that year in attacks where the bomber’s gender was ascertained.

From June 2014 to the end of February of this year, the group deployed 469 female suicide bombers who killed more than 1,200 people and injured nearly 3,000 others.

That means that Boko Haram has now used, by a significant margin, more female suicide bombers than any other terrorist group in history.

There is no evidence, however, that a Chibok girl has ever been a bomber. Boko Haram probably considered them too valuable for such use.

The international outpouring of horror over the kidnappings, however, likely alerted the group to the power of using females, particularly girls, in attacks, and spurred the use of its awful new tactic.

There are other reasons Boko Haram uses women for these types of attacks. Women are generally viewed with less suspicion than men are, and Nigerian cultural norms forbid a man from touching a woman in the way required to search for explosives.

The clothing worn by Nigerian women can also more easily conceal an explosive device. Boko Haram has even begun experimenting with male suicide bombers disguising themselves as females. It also wants to reserve male fighters for combat-related roles.

The evolution of Boko Haram’s bombing campaign also includes the increasing use of children. The group sees them as “cheap labor,” easily replenished through kidnappings, and has at least twice deployed girls as young as 7 as suicide bombers.

Children have many of the same tactical advantages females do when carrying out attacks. The public views them as unthreatening, making it easier to avoid detection while reaching the target.

Children are often easy to coerce or manipulate, particularly those ripped from their families in kidnappings.

Some Boko Haram members may even offer their own children as bombers as a sign of allegiance to the cause. Children that grow up in the group are likely indoctrinated as well to glorify extreme violence, and some may aspire to be suicide bombers.

There are also increasing reports of Boko Haram fighters, including children, being drugged with Tramadol, a synthetic opioid popular in West Africa. That’s presumably to make them more willing to launch dangerous attacks, including suicide bombings.

Other findings from the West Point studies include the fact that female bombers usually attack different types of targets than men do.

Female bombers frequently target secular civilian areas, such as markets and camps for internally displaced people. Men, however, most commonly attack government institutions and religious sites, such as churches and mosques.

Boko Haram has lost much of the territory it once controlled in northeast Nigeria, but its continued ability to launch attacks demonstrates that it is far from defeated.

The Nigerian government has failed to make sufficient progress addressing the non-military components of the Boko Haram threat.

The government has not done enough to help moderate Muslims to fight back against Boko Haram’s radical Islamist ideology, nor has it made sufficient progress in addressing the political and socioeconomic grievances in northeast Nigeria that make the group appealing to some.

That only makes it likely the group, and its horrifying use of suicide bombers, will continue for the foreseeable future.