Repeatedly in my interviews, the surface reasons these men joined the cause, such as perceived American hostility to Islam or the American involvement in Iraq or Afghanistan, often masked a personal sense of alienation and individual crisis that gripped their lives, from a failed love affair or family conflict to not being able to relate to their peers.

The radical Islam cause provides the relief from their crisis. It serves as the easy outlet to unleash their demons. They can now achieve a greater glory. Their lives now matter. They can become overnight heroes, featured in the media, endowed with fame and celebrated among their small, closed circle—either online or among fellow believers.

Whether the Tsarnaev brothers were self-radicalized through the Internet or by other individuals in the United States or overseas, they tapped into a belief system that feeds on vulnerable young men. It is this radical interpretation of Islam and its ideology—which demonizes nonbelievers and creates an exclusivist community—that poses an all too real danger and cannot be defeated by force of arms alone.

I met many young men who ended up leaving the radical movement. The reason each of them left centered on their own realization that al Qaeda and others were engaged in corruption or deception and did not represent true Islam.