Introduction to the 9·11 incident: At 8:40 a.m. Eastern Time on September 11, 2001, four U.S. domestic flights were hijacked almost simultaneously, and two of them crashed into the World Trade Center skyscraper in Manhattan, New York. In the center, a plane attacks the Pentagon in Washington, D.C., home to the U.S. Department of Defense. Two 110-story buildings at the World Trade Center collapsed one after another after being attacked. Many nearby buildings also collapsed due to the earthquake, and part of the Pentagon's structure was engulfed by fire. The terrorist attacks on September 11, 2001 had a huge and immediate impact on the United States. Various commemorative activities were held around the world after the incident, and rescue activities lasted for several months.