Discussing the Boston Marathon bombers, Vice President Joe Biden aptly asked, “Why do they do what they do?” Tamerlan Tsarnaev was apparently influenced, in part, by the doctrine of Anwar al-Awlaki. Al-Awlaki, a dual U.S.-Yemini citizen affiliated with al Qaeda in the Arabian Peninsula, was killed in a drone attack in Yemen with fellow violent jihadi propagandist Samir Khan, who edited the online magazine Inspire.

Younger brother Dzhokhar cited Inspireas ideological inspiration and the recipe for their improvised explosive device.

Tamerlan also spent some six months in Dagestan, Russia, where extremist Chechens might have influenced him. Other reports reference a Boston-area Armenian convert named Misha, who might have influenced Tamerlan, leading him to abandon boxing, music, and embrace violent tenets. Tamerlan, in turn, is believed to have swayed Dzhokhar.Against this backdrop, it is important to appreciate how individuals are brought into the folds of radicalism so that terrorism will occur less frequently.

Radicalization is the process of embracing an extremist belief system, including the inclination to use, support, or facilitate violence, as a way to effect political, ideological, religious, or social change. A group’s propaganda—delivered in visual, tactile, audio, and in-person forms—is disseminated to alienated or aggrieved individuals. This portion of the populace is more readily respond to these radical messages than the general population.

Extremist ideals are contrasted with status quo approaches and traditional precepts of what is right and wrong. A crucial part of this message is the permissibility to use violence to hasten change. Individuals can be radicalized as a result of exposure to terrorist ideologies in various settings.

Radicalization can arise from the influences of immediate and extended family by they based domestically or internationally. It can occur from exposure at secular and religious educational institutions at all levels. This radicalization can occur through interactions with fellow students, faculty, staff as well as student organizations, whatever their ideological tint.

At religious institutions individuals can be exposed to firebrand clergy and zealous congregants. Such exposure can manifest itself in fringe doctrine shared face-to-face, audio, video, and text, in their native tongue or in foreign languages.

Extremist precepts are often articulated in texts that are the cornerstone or reference guides of terrorist groups. Radicalization can materialize after protracted interplay with friends, whether they first meet in local, overseas, or online communities. Initial receptivity towards friendship may be shaped due to an array of commonalities, be they racial, ethnic, religious, ideological, socio-economic, geography, language, employment, education, or otherwise.

Other modalities for radicalization include exposure to neighbors, who by their proximity, frequency of contact, and shared scenery can influence individuals to embrace a particular extremist mindset. One’s place of employment, and colleagues there, are additional routes for radicalization as shared experiences and time spent together can be leveraged. Further exposure to radical ideas can take hold during interactions with individuals at various activities, including clubs, civic organizations, and political organizations.

Additional venues, including sporting events, gun shows, political rallies, youth centers, gymnasiums, and recreational activities such as paintball, are settings where radicalization took shape. Paintball was an activity that aided in radicalizing and meshing the 2005 London suicide bombers. Additional opportunities for radicalization occur during youth and summer camps as well as during paramilitary training.

Prisons are used to radicalize individuals in extremist philosophies, such as advocating violence to achieve political goals. Abu Musab al-Zarqawi, the late leader of al Qaeda in Iraq, was radicalized in al Qaeda-related ideologies while serving in a Jordanian prison.

Individuals can also be exposed to extremist beliefs of government leaders, political parties, and individual politicians. Diverse radical perspectives are disseminated worldwide, around-the-clock, in different languages through disparate formal and informal media outlets, including print, radio, cable and satellite television, and online.

Terrorist groups use the Internet to share text, video, and audio of all types of communications in a rapid, inexpensive, and effective manner.  Their websites and Internet properties (e.g., social networking sites as well as audio and video content) enable them to diffuse broad areas of data: information about the group, its goals, leaderships’ perspectives, doctrine, frequently asked questions, including explanations of what problems exist and how their movement will address them. They offer online forums, online content (books, reports, newsletters, etc.), videos, images, and online music that support their doctrines and aid in radicalization of viewers.

Fully understanding how the Tsarnaev brothers came to embrace the tenets of violent jihad should enable the U.S. government to redouble its counter-radicalization efforts. Failure to do so effectively will result in us witnessing future Boston-like incidents arising undertaken by terrorists from diverse ideological reference points.

* Dean C. Alexander is director, homeland security research program and associate professor at Western Illinois University.