Definitions
A working definition of homeland security is the national effort by all levels of government to protect the territory of the US from hazards, internal and external, natural and man-made.
One of the stated purposes of the US Constitution appears in the preamble: “We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, promote the general welfare, and provide for the common defense…”
The federal definition of Homeland Security appears in The National Strategy for Homeland Security of October 2007:
“Homeland security is a concerted national effort to prevent terrorist attacks within the United States, reduce America’s vulnerability to terrorism, and minimize the damage and recover from attacks that do occur.”
The term, “homeland defense,” was frequently used to describe the above mission from 1997 through late 2000, and today reflects the role of the Department of Defense in homeland security. Whereas homeland security encompasses policies, actions, and structures designed to accomplish the above mission while protecting the rights and freedoms inherent in the U.S. Constitution, homeland defense is essentially a subset of homeland security with supporting policies and actions designed to defend against extra-territorial threats, and to provide selective military assistance to civil authorities.
The Quadrennial Homeland Security Review defines homeland security in an even broader context, as a distributed and diverse national enterprise: the homeland security enterprise refers to the collective efforts and shared responsibilities of Federal, State, local, tribal, territorial, nongovernmental, and private-sector partners—as well as individuals, families, and communities—to maintain critical homeland security capabilities. It connotes a broad-based community with a common interest in the safety and well-being of America and American society.