One major effect of September 11th was a huge increase in security and surveillance, especially in air travel and government policy. After the attacks, the United States created the Department of Homeland Security and passed the USA PATRIOT Act, which expanded government powers to monitor communications in the name of preventing terrorism. Airport security was completely overhauled: passengers began going through stricter screening, new limits were placed on what could be carried on planes, and federal agencies took over airport security operations.

Beyond security, 9/11 also led to long‑term wars in Afghanistan and Iraq, reshaped U.S. foreign policy around counterterrorism, and caused lasting physical and mental health problems for first responders and people living near Ground Zero.