Last week’s horrific Islamic State-linked terrorist attacks in Paris illustrate another troubling phenomenon: family-affiliated terrorist activities occurring globally. More specifically, French nationals and brothers Ibrahim and Salah Abdeslam participated in carrying out the attacks, with the former conducting a suicide bombing at a Paris restaurant, and the latter renting a car that delivered attackers to Bataclan concert hall. Salah and several co-conspirators eluded French authorities. Now an international fugitive, Salah served time in prison for armed robbery with the mastermind of the Paris attacks Belgian Abdelhamid Abaaoud.

Abaaoud was killed this week in Paris with his cousin, Hasna Aitboulahcen, during a police raid. Aitboulahcen detonated a suicide bomb belt, while Abaaoud’s demise arose from either blowing himself up or during gunfire exchange with police. Previously, Abaaoud recruited his 13-year-old brother to join the Islamic State.

In the United States—as internationally—families have been enticed by Islamic State propaganda. For instance, this year a Mississippi couple (Jaelyn Delshaun Young and Muhammad Oda Dakhlalla), a Texas family (Wolfe) comprising a husband, wife, and their children, and three Illinois siblings (Khan), including two minors, were detained at different airports while trying to join the self-declared caliphate.

Likewise, in 2015, brothers Alaa and Nader Saadeh, as well as three others, allegedly conspired to travel to Syria and join the Islamic State. Last year, German authorities intercepted two Colorado teenage sisters and their female schoolmate after they arrived at Frankfurt Airport en route to Turkey while intending to reach the Islamic State. This March two Illinois cousins (Hasan and Jonas Edmonds) were arrested for allegedly planning to travel to Syria and join the caliphate (Hasan). Jonas intended to kill over 100 people while conducting a terror attack against the Joliet Armory.

Other noteworthy terrorists in this family-linked milieu include Charlie Hebdo magazine assassins Cherif and Said Kouachi, Boston Marathon bombers Tamerlan and Dzhokhar Tsarnaev, and three sets of brothers who served as hijackers on 9/11. There are numerous frameworks by which to analyze the prevalence of extremist/terrorists in family units.

This type of deviancy, occurring within the rubric of social networks, is not new. Terrorism within family units is a manifestation that has occurred throughout the world. The full spectrums of familial relations have been witnessed in this form of political extremism.

Such radicalization has materialized across diverse ideologies: from religiously motivated precepts to national liberation and from hate-based ideologies to other perspectives. Family frameworks enable higher instances of conversion to radical beliefs given the imprimatur of credibility and trust that attach there versus unaffiliated networks.

A broad variance has been observed regarding the backgrounds of the family members, including such factors as: socio-economic, race, religion, ethnicity, national origin, and foreign-affinity-links. Family participation in terrorism pervades all types of group structures—hierarchical and networked—and includes unaffiliated cabals. It includes different levels of group participation: leaders, operational cadre, active supporters, and passive supporters. Various types of terror attacks have been undertaken by family-linked terrorists including: bombings, suicide bombings, and gunfire, among others, with variances in operational stage.

Existing terror ties within the family network have been expanded through incorporating additional family members through marriage. In this way, a broad array of additional recruits or sympathizers may arise as networks of expanding families can be tapped. Still, family affiliated terror groups may involve membership outside of the family setting as well.

Patriarchs tend to have a strong influence on the level of radicalization and recruitment of family members. Widows and other female survivors of their kin perceived as victims of state oppression sometimes, too, embrace violence. Most prominently is the case of the Black Widows of Chechnya. In some cases, the extremist activities are unknown to all the family members until after the terrorist act takes place.

Threats arising from family-connected terrorism must be understood and undermined, whether aligned with the Islamic State, al Qaeda, or other terrorist groups. Sadly, last week’s Paris attacks, as the Charlie Hebdo, Boston Marathon, and September 11 terror incidents before, are bloody reminders of this terror phenomenon.

* Dean C. Alexander is professor/director of the Homeland Security Research Program at Western Illinois University. He recently co-authored The Islamic State: Combating the Caliphate Without Borders (Lexington Books, 2015).