Landmark Law U.S. Department of Homeland Security On September 11, 2001, the World Trade Center buildings in New York City were destroyed, and the Pentagon in Washington, DC was damaged by terrorist attacks. In 2002, Congress enacted the Homeland Security Act (HSA), which created the federal cabinet-level U.S. Department of Homeland Security (DHS). The creation of the DHS was the largest government reorganization in more than 50 years. The act placed 22 federal agencies with approximately 200,000 employees under the umbrella of the DHS, which is the second-largest government agency after the Department of Defense. The DHS contains the Bureau of Customs and Border Protection, the Bureau of Citizenship and Immigration Services, the U.S. Secret Service, the Federal Emergency Management Agency, the Federal Computer Incident Response Center, the National Domestic Preparedness Office, the U.S. Coast Guard, and portions of the Federal Bureau of Investigation, Treasury Department, Commerce Department, Justice Department, and other federal government agencies. The mission of the DHS is to enforce laws to prevent domestic terrorist attacks and related criminal activities, reduce vulnerability to terrorist attacks, minimize the harm caused by such attacks, and assist in recovery in the event of a terrorist attack. The DHS provides services in the following critical areas: (1) border and transportation security, including protecting airports, seaports, and borders and providing immigration and visa processing; (2) chemical, biological, radiological, and nuclear countermeasures, including metering the air for biological agents and developing vaccines and treatments for biological agents; (3) information analysis and infrastructure protection, including protecting communications systems, power grids, transportation networks, telecommunications, and cyber systems; and (4) emergency preparedness and response to terrorist incidents, including training first responders and coordinating government disaster relief.