The event that took place on September 11, 2001 is The two towers of the World Trade Center collapsed after being hit by planes hijacked by terrorists.
The September 11, 2001 is also called the nine eleven attact(9/11), an Islamic sect planed and hijact four comercial jets which where used to reck havoc on the pentagon world trade centers.
It is described as the worst terrorist attack on the United States Ever.
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On September 11, 2001, nineteen terrorists who were members of al-Qaeda, an Islamist extremist network, hijacked four commercial airplanes. In a coordinated attack, the hijackers intentionally flew two of the planes into the Twin Towers of the World Trade Center, and a third into the Pentagon.