The pivotal event that happened on September 11, 2001, was the series of terrorist attacks carried out by the militant group al-Qaeda against the United States. Four commercial airplanes were hijacked, two of which were flown into the Twin Towers of the World Trade Center in New York City, while another crashed into the Pentagon. The attacks resulted in significant loss of life and triggered a global response, including the War on Terror and the subsequent invasions of Afghanistan. This event had lasting repercussions on U.S. foreign policy and national security.