United States civil defense refers to the use of civil defense

Civil defense

Civil defense, civil defence or civil protection is an effort to protect the citizens of a state from military attack. It uses the principles of emergency operations: prevention, mitigation, preparation, response, or emergency evacuation, and recovery...

 in the history of the United States

History of the United States

The history of the United States traditionally starts with the Declaration of Independence in the year 1776, although its territory was inhabited by Native Americans since prehistoric times and then by European colonists who followed the voyages of Christopher Columbus starting in 1492. The...

, which is the organized non-military effort to prepare Americans for military attack. Over the last twenty years, the term and practice of civil defense have fallen into disuse and have been replaced by emergency management

Emergency management

Emergency management is the generic name of an interdisciplinary field dealing with the strategic organizational management processes used to protect critical assets of an organization from hazard risks that can cause events like disasters or catastrophes and to ensure the continuance of the...

 and homeland security

Homeland security

Homeland security is an umbrella term for security efforts to protect states against terrorist activity. Specifically, is a concerted national effort to prevent terrorist attacks within the U.S., reduce America’s vulnerability to terrorism, and minimize the damage and recover from attacks that do...

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There is little history of civil defense in the United States before the twentieth century. Indeed, since time immemorial cities built walls and moats to protect from invasion and commissioned patrols and watches to keep an eye out for danger.