Homeland Security Act
The Homeland Security Act of 2002 was a massive piece of American legislation adopted in reaction to the September 11, 2001 attacks. The purpose of the Act was to strengthen the country against terrorist attacks. President George W. Bush supported the bill and obtained its passaged from a Democratic-controlled U.S. Senate.
The Act is explained in detail on the White House website. Simply put, the Act created a new Department of Homeland Security, defined its primary missions and responsibilities, and created its principal offices.