Juvenile Radicalization Into Violent Extremism: Investigative and Research Perspectives. 
At least since the September 11, 2001 (9/11) terrorist attacks on America, Western countries have ranked terrorism as a high-priority security threat.  Many Western nations have viewed violent extremism principally as an external threat-committed on or against one's homeland by individuals who have migrated or traveled from a foreign country.  More recently, however, concern has accelerated about violent extremism emerging from people who have been born in, or at least spent considerable time as a resident of, the target country.  This has been labeled "homegrown violent extremism" (HVE).