Civil defense, civil defence (see spelling differences) or civil protection is an effort to protect the citizens of a state (generally non-combatants) from military attacks and natural disasters. It uses the principles of emergency operations: prevention, mitigation, preparation, response, or emergency evacuation and recovery. Programs of this sort were initially discussed at least as early as the 1920s and were implemented in some countries during the 1930s as the threat of war and aerial bombardment grew. It became widespread after the threat of nuclear weapons was realized.
Since the end of the Cold War, the focus of civil defense has largely shifted from military attack to emergencies and disasters in general. The new concept is described by a number of terms, each of which has its own specific shade of meaning, such as crisis management, emergency management, emergency preparedness, contingency planning, emergency services, and civil protection.
In some countries, civil defense is seen as a key part of "total defense". For example, in Sweden, the Swedish word totalförsvar refers to the commitment of a wide range of resources of the nation to its defense - including to civil protection. Respectively, some countries (notably the Soviet Union) may have or have had military-organized civil defense units (Civil Defense Troops) as part of their armed forces or as a paramilitary service.