Jihadist extremism in the United States (or Islamist extremism in the United States) refers to Islamic extremism occurring within the United States. Islamic extremism is adherence to a fundamentalist interpretation of Islam (see Islamic fundamentalism), potentially including the promotion of violence to achieve political goals (see Jihadism). In the aftermath of the September 11, 2001 terror attacks, Islamic extremism became a prioritized national security concern of the United States government and a focus by many subsidiary security and law enforcement entities. Initially, the focus of concern was on foreign terrorist groups, particularly al-Qaeda, but in the course of the years since 9/11 the focus has shifted more towards Islamic extremism "within" the United States. The number of American citizens or long-term residents involved in extremist activity is small, but nevertheless is a national security concern.