What do you know about 9/11?

This was a terrorist attack in 2001 which caused the deaths of thousands of individuals. It was caused by the crashing of planes into 2 twin towers of the world Trade Center which was done by hijacked planes by the terrorist group Al Queda. This attack killed almost 3000 people and spread pain throughout the whole United States. 

Bruce Hoffman (2002) Rethinking Terrorism and Counterterrorism Since 9/11, Studies in Conflict & Terrorism, 25:5,303-316, DOI: 10.1080/105761002901223