Any discussion concerning acts of terror has to begin with the September 11, 2001 attacks. By any measure, it was the most brazen and deadliest terrorist attack in recorded history.
Initiated by Al Qaeda, and its leader Osama bin Laden, the attacks led to America's current War On Terror.
The attack itself was a coordinated affair: nineteen members of Al Qaeda managed to hijack four airliners.
Two of these planes crashed into New York City's World Trade Center. A third plane crashed into the Pentagon in Washington DC.
The fourth plane, which is believed to have been headed for targets in Washington DC as well, crashed into a field in Summerset County, Pennsylvania, after passengers attempted to regain control of the plane from the hijackers.
9/11 is the most lethal attack carried out against the US, and continues to have ramifications in the nation's foreign and domestic policies.
