A disaster-response worker gazes at the wreckage of the World Trade Center in New York City in October 2001. 

Photograph by Paul Morse, courtesy U.S. National Archives

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  • On Sept. 11, 2001, Islamic terrorists from a group called al-Qaeda crashed commercial airplanes into the “Twin Towers” of New York City’s World Trade Center, the Pentagon in Washington, D.C., and a field in rural Pennsylvania. More than 3,000 people died.

    This was the most violent attack on the United States since Pearl Harbor in 1941, and the deadliest terrorist attack in U.S. history. The attacks were so shocking they are known by their date alone: 9/11. President George W. Bush made national defense and counterterrorism a priority after the attacks.

  • Term Part of Speech Definition Encyclopedic Entry
    commercial Adjective

    having to do with the buying and selling of goods and services.

    Islam Noun

    religion based on the words and philosophy of the prophet Mohammed.

    Pentagon Noun

    (Arlington, Virginia) huge office building that is the headquarters of the U.S. Department of Defense.

    rural Adjective

    having to do with country life, or areas with few residents.

    terrorist Adjective

    having to do with the use of non-military violence and/or threats of violence to achieve or advocate political change.

    World Trade Center Noun

    office building complex in lower Manhattan, New York, dominated by the Twin Towers until terrorist attacks on Sept. 11, 2001, destroyed them.