The keyword term "sep 11 us attack" functions grammatically as a noun phrase. The core word, or head of the phrase, is the noun "attack." The preceding elements, "sep 11" (an abbreviation for the date September 11) and "us" (an abbreviation for United States), act as noun adjuncts or adjectival modifiers that specify the time and target of the event. Therefore, the principal part of speech for the entire term is a noun.
This noun phrase refers to the series of four coordinated terrorist attacks by the Islamic extremist group al-Qaeda against the United States on the morning of Tuesday, September 11, 2001. The assailants hijacked four commercial airliners. Two of the planes were crashed into the North and South Towers of the World Trade Center complex in New York City, leading to their collapse. A third plane was crashed into the Pentagon in Arlington, Virginia. The fourth plane, after passengers and crew fought back against the hijackers, crashed into a field in Shanksville, Pennsylvania, before it could reach its intended target in Washington, D.C.
The event is of profound historical significance, representing the deadliest terrorist attack in world history and resulting in 2,977 fatalities. The immediate consequence was the initiation of the U.S. "War on Terror," which included the invasion of Afghanistan to depose the Taliban regime that had harbored al-Qaeda. The attacks led to lasting changes in global security, civil aviation protocols, government surveillance powers through legislation like the USA PATRIOT Act, and the establishment of the Department of Homeland Security. It fundamentally reshaped American foreign policy and national consciousness in the 21st century.
