From the Summary: "In 2001, in the wake of the terrorist attacks of September 11, 'homeland security' went from being a concept discussed among a relatively small cadre of policymakers and strategic thinkers to one broadly discussed among policymakers, including a broad swath of those in Congress. Debates over how to implement coordinated homeland security policy led to the passage of the Homeland Security Act of 2002 (P.L. 107-296), the establishment of the Department of Homeland Security (DHS), and extensive legislative activity in the ensuing years."
CRS Report for Congress, R45701
Congressional Research Service: https://crsreports.congress.gov/