The term functions as a compound noun, a specific name for a series of four coordinated terrorist strikes carried out by the Islamic extremist group al-Qaeda against the United States on the morning of Tuesday, September 11, 2001. This proper noun identifies the historical event where 19 terrorists 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, a third plane was crashed into the Pentagon in Arlington, Virginia, and the fourth plane crashed in a field in Shanksville, Pennsylvania, after passengers and crew attempted to regain control.
Grammatically, "September 11th" acts as an adjectival noun or a noun adjunct, modifying the head noun "attack." This structure links the date inextricably with the action, creating a singular conceptual unit that refers exclusively to these events. The strikes resulted in 2,977 fatalities, over 25,000 injuries, and substantial long-term health consequences, in addition to at least $10 billion in infrastructure and property damage. The collapse of the World Trade Center towers caused catastrophic destruction and remains the deadliest terrorist incident in world history.
The designation of this event with a specific, nominal phrase has significant implications. It serves as a historical and cultural touchstone, marking a definitive turning point in U.S. foreign policy and domestic security. The immediate response included the launch of the "War on Terror," the 2001 invasion of Afghanistan to depose the Taliban which had harbored al-Qaeda, and the 2003 invasion of Iraq. Domestically, it led to the passage of the USA PATRIOT Act and the creation of the Department of Homeland Security, fundamentally reshaping national security protocols, air travel, and public surveillance.
