In recent times, many terrorist attacks have been carried out by young men who knew they would die in the attack. This disturbing form of violence became a global concern after 9/11. The U.S. government has spent millions of dollars since then on the study of terrorism, and a new cadre of investigators is striving for quantitative rigor and testable theories. The study of suicide terrorism in particular has been a growth area. The work has challenged some long-accepted notions-for example, that terrorists are pathological, driven by religious fanaticism, or spurred by poverty.