Why is September 11, 2001, a significant date in US history?

On September 11, 2001, members of al-Qaeda hijacked passenger planes and carried out coordinated terrorist attacks in the United States, killing thousands of people. This is why the date is remembered as the day of the largest terrorist attack against the United States. Osama bin Laden was killed in 2011, and the other events listed did not occur on September 11, 2001.

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