Today the United States is undergoing a great transformation in national security thinking and priorities. Between the end of the Cold War in 1989 and the collapse of the Soviet Union in 1991, the country began to abandon the policy of containment and the strategy of deterrence that had governed American relations with the rest of the world for over four decades. For only the fourth time in its national history, the United States has been changing its national security policies and reconfiguring its military institutions to adapt to a new role in world politics.1 Once again, for a variety of reasons not least because of technologies Americans themselves pioneered, defense of the American homeland has become central to national security. Protecting the American people inside the United States is the most significant and perplexing of the changes underway in national defense. What should be-must be-the role of the military in homeland defense?
I. HISTORICAL EXPERIENCE
Until the middle of the 20th century, safeguarding the continental United States and American territories overseas was the primary mission of the American military. The very first American military forces, the colonial militias, came into existence precisely for the purpose of homeland defense, adapted from the citizen military forces of early modern England which themselves had been formed for defense against invasion in the absence of a standing army. In North America beginning in the second quarter of the 17th century, colonial governments required the service of the able-bodied white male population to muster periodically, keep arms, train, and embody not only for defense but for offensive expeditions against hostile Indian tribes. In the 18th century, during the wars between England and France for imperial domination, the threat metastasized into the combined invasion of French and sometimes Spanish forces from the sea as well as on land. The scale and scope of these conflicts forced the colonies to depend on British military forces, and on occasion to fully mobilize the human and material resources of their own populations. So focused on defense were these militia forces that they were almost always restricted by law to service within the colony. At the same time, volunteers or men drafted from the units were used for offensive expeditions to attack Indian tribes, or to seize the seaports, cities, or fortifications of other European powers in the new world.2
Through the 19th century, these local militias-either in the form of the enrolled units (the entire militia of a colony or state), a group of individual volunteers, drafted individuals, or through the concept of a citizen's obligation to serve when required-formed the basis of American military power. After the Civil War, with the creation of state national guards (volunteer militia), the militias began their transformation into the war-fighting reserves of the regular armed forces.3 Beginning in the 1970s, the reserves became even more closely aligned with the regulars in the "Total Force" policy;4 some ground units were assigned to fill out regular Army divisions to make them ready for combat, and some support functions like civil affairs migrated almost entirely into the reserve components.5 In the case of the Air Force, reserve forces grew increasingly integrated into virtually all the combat and support operations of the regulars over a generation's time.6 In the 1990s, National Guard and reserve ground forces began to supplement regular Army forces in peacekeeping and peace enforcement duties overseas, an unprecedented use of reserves in constabulary duties in addition to their other duties.7 The Guard and Reserve leadership grasped every mission available to prove the military importance of reserve forces and to acquire the most resources and most modern weapons possible.8 The regulars, stretched thin after the Cold War by numerous foreign interventions and peacekeeping operations, welcomed the relief from the stresses that a high operational tempo had placed on their personnel and equipment. …