Terrorist attacks are at the forefront of the media cycle—despite being rare in most world regions and claiming considerably fewer lives than other types of homicide. Globally, homicide accounts for roughly half a million deaths per year (see UNODC’s Global Study on Homicide). The majority of homicide victims are thereby killed in interpersonal settings. This includes, for example, victims killed by intimate partners and family members as well as victims killed in criminal contexts. Terrorist attacks, in spite of their dramatic effects, claim considerably less lives, totaling about 38,000 victims per year throughout the world (according to the Global Terrorism Database).

Terrorism is widely considered a form of collective violence. The vast majority of casualties can be attributed to attacks that occurred in the context of hard conflict and war, notably in the Middle East, North Africa, South Asia and in Sub-Saharan Africa. More than for interpersonal types of homicide, numbers for casualties from terror attacks are susceptible to varying greatly from year to year. In Western Europe, for example, roughly 175 victims were killed in terrorist attacks in 2015. That was the highest number of casualties experienced in over a decade and marked an increase of almost thirty times as compared to 2014—but amounted to only a small share of the victims that were killed globally during the same year

Now, why would there be a connection between terrorist attacks and interpersonal forms of homicide?—And why does it matter?

The relationship of collective and interpersonal violence has long been discussed in the context of war. In criminology, the topic has typically received attention after major wars with Western involvement, but has largely been abandoned following the Vietnam war. In 1976, Dane Archer and Rosemarie Gartner (Violent Acts and Violent Times) argued that war—taking the form of “homicide legitimated by the highest auspices of the state”—may legitimate violence and as such “influence the threshold for using homicide as a means of settling conflict in everyday life”. This developed into the so-called legitimation-habituation model. In other words, when role models in state and society advocate violent responses to terrorism (e.g. “war on terror”), citizens may consider violence a legitimate means in their everyday lives. Elevations in everyday violence may thus be thought of as a side product of legitimation of violence. Apart from that, citizens may merely internalize their knowledge of violent attacks to society (habituation and generalization). The more violence is exemplified to them, the more they would be tempted to resort to violence themselves. To put it simply, one could ask: Because a war broke out or a terrorist attack occurred, do more men and women engage in violent attacks, for example killing their intimate partners or committing violent crimes?

So far, it has rarely been readdressed how terrorism may relate to the legitimation and habituation of violence. This is surprising, given not only the prominence that terrorism enjoys as a topic in both research and the media, but also how increasingly blurred the lines between war and terrorism have become in the context of contemporary conflicts and the “war on terror”. Indeed, the triangle of war, terrorism and homicide is an intricate subject of study—that similarly bears imminent societal relevance. Violence has been recognized as a main obstacle to global development. An integrated understanding of violence is thereby needed to design effective counterstrategies and break contagions of violence whatever form they may take.