The United States Department of Homeland Security  is a cabinet department of the United States federal government with responsibilities in public security, roughly comparable to the interior or home ministries of other countries. Its stated missions involve anti-terrorism, border security, immigration and customs, cyber security, and disaster prevention and management. It was created in response to the September 11 attacks and is the youngest U.S. cabinet department. In fiscal year 2017, it was allocated a net discretionary budget of $40.6 billion. With more than 240,000 employees, DHS is the third largest Cabinet department, after the Departments of Defense and Veterans Affairs. Homeland security policy is coordinated at the White House by the Homeland Security Council. Other agencies with significant homeland security responsibilities include the Departments of Health and Human Services, Justice, and Energy. The former Secretary, John F. Kelly, was replaced by Secretary Kirstjen Nielsen on December 5, 2017.

What was formed as a reaction to 9/11?
Department of Homeland Security