Read more: Dissident IRA bomb hidden in child’s bicycle in Belfast

In a new book "Bombshell: The Many Faces of Female Terrorists,” academic Mia Bloom disproves the idea that women involved in terrorism are pawns of male-dominated terrorist groups. The Penn State researcher says they are motivated by more complicated and diverse reasons, including those who acted with the IRA.

Bloom said, "It's true that some women are coerced, but the truth is that motivations vary from terrorist group to terrorist group.  For example, of the women in the provincial Irish Republican Army group that I talked to, not one was coerced; they were enthusiastic about their roles."

Bloom, who is a fellow at the International Center for the Study of Terrorism, looks at the female participation in the world's most recognized terrorist groups in her book. She explains that there are five reasons why females get involved in terrorism:  revenge, redemption, relationship, respect and rape.

She writes, "Relationship, the third R, is particularly crucial in understanding how women are mobilized…The best single predictor that a woman will engage in terrorist violence is her relationship with a known insurgent or jihadist."

Leaders of terrorist groups encourage female participation in their organizations for several reasons. Women are more effective at attracting media attention. They are also held up as an example to goad males into joining with or increasing their participation in terrorist movements.

"Groups have found it very effective to use women as propaganda tools, especially to appeal to men," Bloom explained. "The message is if you don't step up, you're not a man."

Bloom also said that women's participation in terrorism changes from culture to culture and group to group. In some terrorism groups the women assume a leadership role. For example, Ah-lam al-Tamimi, a member of Hamas, planned one of the deadliest terrorist attacks in the history of Israel.

Bloom said, "Some terrorist groups go as far as addressing the roles for females in their founding documents."

However, in some other terrorist groups women do hold a lower status and are used as cannon fodder.

"The truly deplorable thing about female suicide bombing is that in many cases women are usually selected to attack civilian targets, or 'soft targets,' " said Bloom. "So women are being used to kill other women and children."

Her book will be available this fall in the U.S.

Read more: Dissident IRA bomb hidden in child’s bicycle in Belfast

Mural dedicated to the IRA, Northern Ireland