The creation of the new cabinet-level Homeland Security agency after 9/11 and the associated identification of a new homeland security mission to prevent, respond to, and recover from terrorist attacks, constituted the largest reorganization in the United States government since World War II.
Total spending from 2001-2011 on Homeland Security was about $649 billion.
Absent the wars, the US would have spent some money on the areas we now identify as homeland security in the last decade, but just not as much. Annual federal spending in this area grew at an average pace of 3 percent during the 1990s. Assuming a similar rate of growth during the first decade of the 2000s in the absence of 9/11, spending would have reached $23 billion by 2011. Homeland security appropriations are thus estimated to have been $369 billion higher than they would have been otherwise.
State and local governments have also spent money on homeland security, but it is difficult to assess how much of that spending has been reimbursed by federal grants. However, a 2003 US Conference of Mayors’ survey estimated that cities nationwide were spending $70 million per week more on homeland security than they had before 9/11.
If federal spending on homeland security had grown at the same rate as other (non-military) federal spending, total appropriations would have been hundreds of billions of dollars lower.
(Page updated as of February 2015)