What the day changed

2,977 people were killed that morning and the deadliest terrorist attack in history reset the assumptions of an entire generation about air travel, national security, and the reach of a non-state actor. The attacks led directly to the U.S. invasion of Afghanistan weeks later, the creation of the Department of Homeland Security, and a redesign of airport security worldwide that persists today. Nearly a quarter-century on, thousands more first responders and survivors have died from illnesses linked to their exposure at the sites — a toll still being counted long after the day itself ended.