The core of the specified keyword phrase is "11 Sep" (September 11), which functions as a proper noun. This specific date is recognized globally for a series of four coordinated terrorist attacks against the United States on September 11, 2001.
The attacks were orchestrated by the Islamic extremist group al-Qaeda. Militants hijacked four commercial airliners, intentionally crashing two 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, United Airlines Flight 93, crashed into a field in Shanksville, Pennsylvania, after passengers and crew attempted to regain control from the hijackers. The events resulted in 2,977 fatalities, making it the deadliest terrorist attack in human history.
The immediate and long-term consequences of the September 11 attacks were profound. The event precipitated the United States' "War on Terror," leading to the invasion of Afghanistan and significant shifts in U.S. foreign policy. Domestically, it prompted the creation of the Department of Homeland Security and the implementation of extensive new security measures, particularly in air travel. The date now serves as a solemn day of remembrance and a symbol of a pivotal moment that reshaped global politics and security in the 21st century.
