The document discusses the events of September 11, 2001 when four commercial airplanes were hijacked by al-Qaeda terrorists and crashed into buildings, resulting in nearly 3,000 deaths. It provides details on the timeline of crashes into the World Trade Center towers and the Pentagon, as well as the efforts to rescue survivors and recover victims in the aftermath. The attacks had major economic and health impacts and led to U.S. military operations against al-Qaeda and Taliban forces in Afghanistan.