Military assistance to civilian authorities is not a new concept. From before the birth of this nation, the military, whether militia or regular or both, has habitually supported local, state, and federal civilian authorities in times of manmade or natural disaster, civil unrest, or other situations. This support was very often questionable in legality and usefulness. Over time, though, numerous laws and directives have transformed this supporting relationship into an institutionalized interdepartmental and interagency coordination and planning process. The changing nature of threats, however, has expanded the scope of the military's responsibilities in support of civilian authorities. This old mission now involves an ever-widening array of diverse military and Department of Defense (DoD) organizations and agencies equipped with new terminology and new, evolving concepts. The United States faces myriad threats today besides those caused by natural phenomenon. Groups opposed to the thrust of the U.S. post-Cold war policies have multiplied in recent years. The openness of the U.S. society provides an opportunity for our enemies to operate with more freedom than they would have in more restrictive venues. Also exacerbating the threats is the global proliferation of cheap Weapons of Mass Destruction (WMD). The Threats can be defined broadly as international or domestic in nature. International threats fall into one of three separate categories: international terrorism, transnational threats, and conventional attacks. Domestic terrorism stems from domestic groups who are based and operate entirely within the United States, its territories, or possessions, and whose activities are directed at elements of the federal, local, or state governments or the U.S. civilian population.
Papers from the Conference on Homeland Protection, October 2000, p.199-208