"The National Strategy for Homeland Security and the Homeland Security Act of 2002 served to mobilize and organize our nation to secure the homeland from terrorist attacks. This is an exceedingly complex mission that requires coordinated and focused effort from our entire society. To this end, the Department of Homeland Security was established to provide the unifying core of the vast national network of organizations and institutions involved in efforts to secure our homeland. Our first priority is to prevent further terrorist attacks within the United States. To reduce vulnerability without diminishing economic security, we gather intelligence and analyze threats, guard our nation's borders and airports, protect our critical infrastructure and coordinate response to the American people during times of disaster."
Defense Technical Information Center (DTIC): http://www.dtic.mil/dtic/