Terrorism has occurred in the United States throughout its history. In recent years, the United States has experienced less terrorism than in other regions, although a terrorist act could occur at any time. The nation has indigenous terrorist groups that support political or social causes or oppose the government and international terrorist groups that gather intelligence and resources and plan terrorist acts. The multiethnic culture of the United States also makes it possible for many international terrorist organizations to obtain support from populations in the United States. Terrorist groups include right-wing groups, such as the Ku Klux Klan and the Aryan Nations and leftist groups, such as the Republic of New Afrika and the May 19th Communist Organization. Terrorism associated with the Puerto Rican independence movement and transnational activities has also occurred. The law enforcement response in the United States has emphasized cooperation among agencies and levels of government, with emphasis on the use of Joint Terrorism Task Forces. 73 reference notes.