World War I introduced use of strategic aerial attacks on civilians as a tool of warfare. Bombing of Great Britain by German forces underscored the need for civilian defense. The Council on National Defense, a presidential advisory board, was established 29 Aug 1916 and focused on coordinating resources and building civilian morale. State governors were asked to create local councils to support goals of the national agency. Council activities continued to focus on mobilization efforts, rather than protection, and at war's end concentrated on demobilization needs. The Council's operations were suspended in 1921.

Rising tension in Europe during the 1930s sparked a renewed interest in civilian defense. In 1933 President Franklin Roosevelt created the National Emergency Council (NEC), whose mission included responsibility for coordinating emergency programs of all federal agencies. The Council of National Defense was revived in 1940, and states were again asked to create local counterparts. Heavy attacks on civilians in Europe raised fears about the likeliness of such attacks in the United States. In 1941 Roosevelt created the Office of Civilian Defense (OCD) to oversee civilian protection.

With the end of World War II and a threat of attack no longer imminent, Harry Truman closed the OCD shortly after being elected president. This complacency was short-lived. Development of the atomic bomb at the end of the war opened the door to disasters of enormous proportions, and as the relationship between the United States and Soviet Union deteriorated the matter of civil defense rose again to the fore.

In the ensuing years, conceptualization of civil defense and whether it would be primarily a federal or local government responsibility shifted with the changes in administration. Truman felt that state and local government should be in charge of civil defense activities, in part to allay public fears that exclusive federal oversight could result in a garrison state. The program concentrated on promoting shelter building, attack warning systems, and public education.

Under President Dwight Eisenhower the focus of civil defense shifted from sheltering to mass evacuation. Economic concerns drove the change in emphasis, but they were aided by world events. Development of thermonuclear weapons, whose destruction was so great, led experts to doubt shelters could protect victims of direct attacks. Nevertheless, some members of congress continued to argue in favor of shelter building. The policy was eventually modified to an evacuation to shelter approach.

Civil defense became a priority under President John F. Kennedy. He favored a nationwide shelter system and made it the centerpiece of his program. Kennedy also promoted an educational system, distributing brochures to the public describing the shelter program and outlining steps to take in the event of an attack. The civil defense program was cut back dramatically after Kennedy's death in 1963. Public interest in the program waned, and a series of natural disasters turned attention to victim assistance over preparedness for enemy attack.

Richard Nixon's administration redefined civil defense policy to include disaster preparedness. Hurricane Camille in 1969 in particular highlighted shortcomings in the nation's plan for disaster response. Little progress was achieved as bureaucratic inefficiencies plagued the program. Gerald Ford continued to follow the dual use approach, but later shifted emphasis to the civil defense aspect.

President Jimmy Carter began a review of the agencies overseeing civil defense when he took office. The nuclear disaster at Three Mile Island in March of1979, and the slow and ineffective response to it, highlighted the need for a single agency to oversee disaster preparedness. Federal Emergency Management Agency (FEMA) was established 20 Jul 1979 to coordinate federal disaster response.

Congress voted in 1981 to amend the 1950 Civil Defense Act to allocate funds for both natural disasters and enemy attacks. Congress disagreed with President Ronald Reagan over concentrating FEMA's planning efforts on evacuation, and wanted more attention to disaster preparedness. In response, FEMA tried to fuse civil defense and planning for natural disasters, but Congress was not convinced that it would be effective and refused to meet requests for additional funding.

During the late 1980's and early 1990's FEMA was directed to develop a multi-hazard approach to planning. However, slow response to Hurricane Hugo in 1992 revealed continued poor performance on the part of the agency, and it was reorganized during Bill Clinton's presidency. An increasing recognition of the threat of terrorist attacks within the United States added urgency to FEMA's mission.

After the terrorist attacks on 11 Sep 2001, the Office of Homeland Security was established to coordinate a national security strategy. President George W. Bush submitted a plan to Congress proposing creation of the Department of Homeland Security (DHS), which was established 25 Nov 2002. Early work in DHS concentrated on terrorist threats, although its mandate included natural and other disasters. In March 2003 FEMA became part of DHS. Hurricane Katrina's 2005 destruction in Alabama, Mississippi and Louisiana revealed significant failures in federal, state and local disaster response, prompting a review of preparedness policies. Civil defense and homeland security continue to evolve as the country adapts to new threats and potential disasters.