The document discusses the September 11th, 2001 terrorist attacks carried out by al Qaeda where 19 terrorists hijacked 4 commercial planes and crashed them into buildings, killing nearly 3,000 people. This was a major terrorist attack on U.S. soil orchestrated by Osama bin Laden and al Qaeda, and prompted the U.S. to launch military operations in Afghanistan and Iraq in the following years. The attacks changed U.S. foreign policy and heightened concerns about terrorist groups acquiring weapons of mass destruction.